Blended membranes for water vapor transport and methods for preparing same

ABSTRACT

Water vapor transport membranes for ERV and other water vapor transport applications are provided. The membranes include a substrate and an air impermeable selective layer coated on the substrate, the selective layer including a cellulose derivative and a sulfonated polyaryletherketone. In some embodiments the sulfonated polyaryletherketone is in a cation form and/or the selective layer includes s PEEK and CA in an s PEEK:CA (wt.:wt.) ratio in the range of about 7:3 to 2:3. Methods for making such membranes are provided. The methods include applying a coating solution/dispersion to a substrate and allowing the coating solution/dispersion to dry to form an air impermeable selective layer on the substrate, the coating solution/dispersion including a cellulose derivative and a sulfonated polyarylether ketone. In some embodiments the sulfonated polyaryletherketone is in a cation form and/or the coating solution/dispersion includes s PEEK and CA in an sPEEK:CA (wt.:wt.) ratio in the range of about 7:3 to 2:3.

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/012,533 to Huizing et al., entitled SULFONATEDPOLYETHER ETHER KETONE COMPOSITE MEMBRANES FOR ENTHALPY EXCHANGE ANDOTHER WATER VAPOR TRANSPORT APPLICATIONS, filed Jun. 16, 2014, assignedto the assignee of the present invention, and incorporated herein bythis reference in its entirety.

FIELD

This application relates to membranes that are selectively permeable. Aparticular application for membranes according to some embodiments isfor water vapor transport. Membranes that selectively pass water vaporhave application, for example, in energy recovery ventilation (‘ERV’)systems.

BACKGROUND

In buildings it is generally desirable to provide an exchange of airsuch that air from inside the building is expelled and replaced withfresh air from outside the building. In colder climates where the insideof the building is much warmer than the outside air (‘heatingapplications’) or in hot climates where the inside of the building isairconditioned and is much cooler than the outside air (‘coolingapplications’) there is an energy cost to this. In heating applicationsthe fresh air is typically both colder and drier than the air inside thebuilding. Energy is required to heat and humidify the fresh air. Incooling applications the fresh air is typically both warmer and moremoist than the air inside the building. Energy is required to cool anddehumidify the fresh air. The amount of energy required for heating andcooling applications can be reduced by transferring heat and moisturebetween the outgoing air and the incoming air. This may be done using anERV system comprising membranes which separate flows of incoming andoutgoing air. The characteristics of the membranes are an importantfactor in the performance of an ERV system.

Ideally a membrane in an ERV system should be: air-impermeable such thatthe membrane can maintain effective separation of the incoming andoutgoing air flows; have a high thermal conductivity for effective heattransfer between the incoming and outgoing air flows; and provide highwater vapor transport for effective transfer of moisture between theincoming and outgoing air flows but substantially block the passage ofother gases. Achieving these characteristics typically favors the use ofthin membranes.

In addition to the above it is desirable that the membranes be robustenough for commercial use, cost effective to produce, and compliant withany applicable regulations. At least some jurisdictions have regulationsthat relate to the flammability of membranes used in ERV systems. Forexample, UL 94 is a standard released by Underwriters Laboratories ofthe USA which relates to flammability of plastic materials for parts indevices and appliances. UL 94 provides additional classifications VTM-0,VTM-1, VTM-2 for thin films. UL 723 is another standard released byUnderwriters Laboratories that provides a test for surface burningcharacteristics of building materials.

There is a need for membranes suitable for ERV applications and/or otherwater vapor transport applications that address some or all of theseissues.

SUMMARY

This invention has a number of aspects. One aspect provides a membranehaving improved water vapor permeability and improved selectivity forwater vapor transport. Such membranes may be incorporated into ERV coresand ERV systems. Another aspect provides ERV cores and ERV systems thatincorporate such membranes.

In some embodiments, water vapor transport membranes are provided. Themembranes include a substrate and an air impermeable selective layercoated on a first surface of the substrate, the selective layerincluding at least one cellulose derivative and at least one sulfonatedpolyaryletherketone. In some embodiments the sulfonatedpolyaryletherketone is in a cation form.

In some embodiments, the cellulose derivative is cellulose acetate (CA)and the sulfonated polyaryletherketone is sulfonated polyether etherketone (sPEEK) and the selective layer includes sPEEK and CA in ansPEEK:CA (wt.:wt.) ratio in the range of about 7:3 to about 2:3.

Another aspect of the invention provides methods for making water vaportransport membranes for ERV applications or for other applications inwhich water vapor transport is required.

In some embodiments, the methods include applying a coating solution ordispersion to a first surface of a substrate and allowing the coatingsolution to dry to form an air impermeable selective layer on the firstsurface of the substrate, the coating solution including at least onecellulose derivative and at least one sulfonated polyaryletherketone. Insome embodiments the sulfonated polyaryletherketone is in a cation form.

In some embodiments, the cellulose derivative is CA and the sulfonatedpolyaryletherketone is sPEEK and the coating solution or dispersionincludes sPEEK and CA in an sPEEK:CA (wt.:wt.) ratio in the range ofabout 7:3 to about 2:3.

Further aspects and example embodiments are illustrated in theaccompanying drawings and/or described in the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate non-limiting example embodiments ofthe invention.

FIG. 1A is a schematic illustration showing a membrane according to anexample embodiment.

FIG. 1B is a schematic illustration showing a membrane according to anexample embodiment.

FIG. 2 is a flow chart which illustrates methods for making membranesaccording to some embodiments.

FIG. 3 is an image of the surface of a sample film according to anexample embodiment.

FIG. 4 is a cross-sectional image of a sample film according to anexample embodiment.

FIG. 5 is an image of the surface of a sample membrane according to anexample embodiment.

FIG. 6 is an image of the surface of a sample film according to anexample embodiment.

FIG. 7 shows an image of the surface of a sample membrane according toan example embodiment.

FIG. 8 shows a cross-sectional image of a sample film according to anexample embodiment.

FIG. 9 shows a cross-sectional image of a sample film according to anexample embodiment.

FIG. 10A is a curve showing the increase in acetic acid crossover ofsample membranes as a function of relative humidity.

FIG. 10B is a curve showing the increase in ethanol crossover of samplemembranes as a function of relative humidity.

FIG. 11 is graph showing the relationship of water vapor sorption torelative humidity of sample membranes.

FIG. 12 is a graph showing the relationship of water vapor desorption torelative humidity of sample membranes.

FIG. 13 is a schematic illustration showing an ERV core according to anexample embodiment.

FIG. 14 is a schematic illustration showing an ERV core in an ERV systemaccording to an example embodiment.

DETAILED DESCRIPTION

Throughout the following description, specific details are set forth inorder to provide a more thorough understanding of the invention.However, the invention may be practiced without these particulars. Inother instances, well known elements have not been shown or described indetail to avoid unnecessarily obscuring the invention. Accordingly, thespecification and drawings are to be regarded in an illustrative, ratherthan a restrictive sense.

List of Definitions

AA crossover—acetic acid permeation.

About—means near the stated value (i.e. within +/−20% of the statedvalue).

Acetyl content—the percentage by weight (%) of acetyl groups incellulose acetate.

Blend—a mixture of a substance with one or more other substances,wherein the substance and the one or more other substances combinewithout chemically reacting with one another.

CA—cellulose acetate. Cellulose acetate is the acetate ester ofcellulose. Cellulose acetate is typically derived from naturallyoriginating cellulose materials. Cellulose acetate may be made byacetylating cellulose materials with acetic acid and acetic anhydride inthe presence of sulfuric acid. The degree of acetylation typicallyranges from about 20 to about 60% (% acetyl content).

CAB—cellulose acetate butyrate.

CAP—cellulose acetate propionate.

Coating loading or coating weight—the basis weight of a selectivepolymer film layer coated on a substrate in g/m². When the coating isapplied as a continuous dense film on a substrate surface, the coatingweight is directly proportional to the thickness of the coating.

DMF—dimethylformamide.

DMSO—dimethyl sulfoxide.

DP—dry-process.

DS—degree of sulfonation. Degree of sulfonation (DS) refers to the ratioof PEEK monomer units in the polymer that contain a sulfonic acid (SO₃H)groups to the total number of PEEK monomer units in the polymer.DS=y/(x+y), where x is the total number of PEEK monomer units in thepolymer that are not sulfonated and y is the total number of PEEKmonomer units in the polymer that are sulfonated. 100% DS means thatevery PEEK monomer unit in the polymer has a sulfonic acid group.

DP-PP—a porous polypropylene substrate made by a dry stretching process.

EATR—exhaust air transport ratio.

EC—ethyl cellulose.

EM—electron microscopy.

ERV—Energy Recovery Ventilation. Energy Recovery Ventilation is used toprovide air exchange in buildings. ERV transfers both heat and moisturebetween outgoing air and incoming fresh air. ERV is performed usingair-to-air heat exchangers that transfer both sensible heat and latentheat.

ERV core—a heat and moisture exchanger assembled from layers or platesof membranes.

IEC—ion exchange capacity.

Microporous—refers to a material having pores with diameters less thanabout 0.5 microns.

M_(N) ca.—number average molecular weight.

MW—molecular weight.

Na-sPEEK—the sodium ion form of sulfonated polyether ether ketone,wherein sulfonic acid group protons are replaced by sodium ions.

NMP—N-methyl-2-pyrrolidone.

PE—polyethylene.

% (percent) porosity—a measure of the void (i.e. “empty” spaces in amaterial), and is a fraction of the volume of voids over the totalvolume of a material as a percentage between 0 and 100%.

Permeance—vapor pressure differential normalized flux (mol m⁻² s⁻¹ Pa⁻¹)or GPU (gas permeance units), where 1 GPU=1×10⁻⁶ cm³ (STP) cm⁻² s⁻¹cmHg⁻¹.

Permeability—thickness and vapor pressure normalized flux (mol-m m⁻² s⁻¹Pa⁻¹) or Barrer, where 1 Barrer=1×10⁻¹⁰ cm³ (STP) cm cm⁻² s⁻¹ cmHg⁻¹.

PTFE—polytetrafluoroethylene.

PEEK—poly(oxy-1,4-phenyleneoxy-1,4-phenylenecarbonyl-1,4-phenylene).PEEK or ‘polyether ether ketone’ is a thermoplastic polymer in thepolyaryletherketone family of polymers. PEEK is commercially availablefrom different producers and at various molecular weights.

Porosity—the total void or open volume of a material.

PP—polypropylene.

RH—relative humidity.

Selectivity—the ratio of the permeance or permeability of one chemicalspecies over another chemical species through a membrane.

SEM—scanning electron microscopy.

SMS—spun-melt-spun. A combined nonwoven fabric comprising two layers ofspunbond combined with a one layer meltblown nonwoven, conformed into alayered product wherein the meltblown layer is sandwiched between thespunbond layers.

Solids content—in reference to a solution or dispersion means the amountof dry material remaining after substantially all solvent in thesolution or dispersion is driven off (e.g. by drying) divided by thetotal mass of material and solvent in the solution or dispersion. Forexample, if 100 milligrams of solution or dispersion is applied to acertain area of a substrate and, after drying, a resulting layer ofsolids weighting 10 mg remains on the substrate then the ‘solidscontent’ of the original solution or dispersion is 10 mg/100 mg=10%.

sPEEK—sulfonated polyether ether ketone. Sulfonated polyether etherketone is a modified type of PEEK, which is sulfonated. The degree ofsulfonation of sPEEK is typically in the range of about 20% to about100%. PEEK polymers can be sulfonated by various methods to add sulfonicacid groups to the polymer chains. Changing the DS in sPEEK causeschanges in permeability, sorption, and solvent solubility properties ofthe polymer.

STP—standard temperature and pressure (0° C., 101325 Pa).

THF—tetrahydrofuran.

VOC—volatile organic compounds.

Weight percent—wt. %. Weight percent (wt. %) refers to the ratio of themass of one substance (m₁) to the mass of a total mixture (m_(tot)),defined as

${{Weight}\mspace{14mu} {percent}} = \underset{m_{tot}}{{{\underset{\_}{m}}_{\underset{\_}{1}}100}\%}$

WP—wet-process.

WP-PE—a porous polyethylene substrate made by a wet formation andstretching process.

WVT—water vapor transport (kg/m²/day or mol/m²/s).

WVTR—water vapor transport rate.

Membrane Structure

FIG. 1A shows a membrane 10 according to an example embodiment. Membrane10 comprises a porous substrate 12 and a selective layer 14 on a surface13 of substrate 12. Membrane 10 is air impermeable and permeable towater vapor. For ERV applications, membrane 10 is preferably much morepermeable to water vapor than it is to other chemical species (e.g.volatile organic compounds). In some embodiments a porous substratecarries thin surface layers of a blend of water-permeable polymers onone surface of the substrate. Since membrane 10 is coated only on oneside, there may be a preferred orientation for the membrane in certainapplications. However, membranes with different properties and watertransport characteristics can be obtained by applying selective layersto both sides of the substrate. In some alternative embodiments a poroussubstrate carries thin surface layers of a blend of water-permeablepolymers on both sides of the substrate.

The permeance of water vapor through membrane 10 is affected by the porestructure and thickness of substrate 12 as well as the structure,composition, and thickness of selective layer 14.

In some embodiments membrane 10 has a thickness in the range of 10 to100 microns, preferably 15 to 50 microns. In some embodiments membranehas a thickness less than 300 microns.

Selective Layer

Selective layer 14 forms a thin but continuous and dense (i.e.substantially free of voids) solid layer on surface 13 of substrate 12.Selective layer 14 acts as a selective barrier to air and contaminantgas transport, but permits the passage of water and water vapor.

For WVT applications, selective layer 14 is preferably sufficientlyflexible to allow handling, pleating, and processing of membrane 10 toform ERV cores or other such devices. For such applications, membrane 10typically operates in the range of about −40° C. to about 100° C.

Selective layer 14 comprises at least one sulfonated polyaryletherketonepolymer blended with at least one cellulose derivative. The at least onesulfonated polyaryletherketone polymer comprises sulfonated polyetherether ketone (sPEEK) in some embodiments. The at least one cellulosederivative may comprise cellulose acetate (CA), cellulose acetatepropionate (CAP), cellulose acetate butyrate (CAB), ethyl cellulose(EC), or combinations thereof, preferably CA. In some embodimentsselective layer 14 comprises sPEEK blended with CA.

In some embodiments selective layer 14 may further comprise desirableadditives such as one or more of: flame retardants, additionaldesiccants, zeolites, inorganic additives (such as silica, titania, andlumina), plasticizers, surfactants, desiccant salts, and microbicides.

In some embodiments the acetyl content of the cellulose derivative isbetween about 20% to about 62%, preferably about 40%. For WVTapplications, the acetyl content of CA may be between about 20% to about62%, preferably about 40%. In general, increasing the acetyl content ofCA tends to increase its solvent resistance and glass transitiontemperature while decreasing its water vapor permeability. Thus, theacetyl content of CA may be selected so that the selective layer hasgood transport properties for vapor separation applications (i.e. one ormore of the following properties: high WVT; low contaminant crossover;and compatibility with a suitable solvent for solubilizing CA and thesulfonated polyaryletherketone polymer such as sPEEK).

In some embodiments the average M_(N) ca. of the cellulose derivative isabout 12,000 to about 122,000. For WVT applications, the average M_(N)ca. of CA may be about 30,000 to about 122,000, preferably about 50,000.

In some embodiments the degree of sulfonation (DS) of the sulfonatedpolyaryletherketone polymer, such as sPEEK, is in the range of about 23%to about 100%, preferably about 60% to about 70%. For WVT applications,the DS of sPEEK may preferably be in the range of about 60% to about70%. Below about 60% DS, the sPEEK polymer may be insoluble inacetone/water and methanol/water solutions. Above about 70% DS, thesPEEK polymer may be soluble in both acetone/water and methanol/watersolutions, but casting thin, dense (i.e. substantially free of voids),and defect-free film layers on microporous substrates may be difficult.Further, above about 70% DS, volatile organic compounds (VOC) crossovermay be increased under high humidity conditions. At very high DS, sPEEKmay be soluble in water.

In some embodiments the average M_(N) ca. of the sulfonatedpolyaryletherketone polymers is about 20,000 to about 180,000. For WVTapplications, the average M_(N) ca. of sPEEK may be about 20,000 toabout 180,000.

In some embodiments the protons of the sulfonic acid groups of thesulfonated polyaryletherketone, such as sPEEK, are exchanged for sodium,lithium, or another cation as described elsewhere herein.

Selective layer 14 may be selected to have the ability to transportwater vapor as well as condensate in the form of liquid water. Watertransport is driven by diffusion through selective layer 14 by aconcentration gradient from a wet side of membrane 10 to a dry side ofthe membrane. The thickness of selective layer 14 affects the rate ofwater transport through it, so that a thicker selective layer will tendto have a lower rate of water transport. Thus, it is desirable to reducethe selective layer thickness in order to increase the water transportrate without unduly compromising the selectivity of the membrane (andthe ability of the membrane to act as a barrier to gas mixing).

In some embodiments the coating loading of selective layer 14 onsubstrate 12 is in the range of about 0.1 g/m² to about 10 g/m²,preferably in the range of about 0.5 g/m² to about 2.5 g/m². In someembodiments the loading of selective layer 14 on substrate 12 is lessthan about 5 g/m².

In some embodiments the thickness of selective layer 14 on substrate 12is in the range of about 0.1 micron to about 10 microns, preferablyabout 0.5 micron to about 2 microns, more preferably about 0.75 micronto about 1.25 microns. In some embodiments the thickness of selectivelayer 14 on substrate 12 is less than about 5 microns.

The selectivity of a material refers to the ratio of the permeance orpermeability of one chemical species over another chemical speciesthrough a membrane. For ERV applications, an important aspect of theselectivity of the membrane is the relative permeability of desiredmolecules (i.e. water vapor) over undesirable compounds (for example,carbon dioxide, VOCs). Polymers with high permeability and highselectivity for water vapor are desirable for use in ERV membranes.However, materials with high permeability for one compound often alsohave high permeability for other compounds (i.e. low selectivity).Further, the presence of humidity in the airstream that is in contactwith the coated surface of a membrane can have a ‘plasticizing’ effectwhen water vapor is absorbed into the polymer film. This can lead todecreased selectivity under high humidity conditions. It is desirable toreduce this effect.

By appropriately selecting the polymer blend of the selective layer onemay alter the functional relationship between water vapor permeabilityand selectivity. In some embodiments the water vapor permeance ofsulfonated polyaryletherketone/cellulose derivative coated membranes isat least about 6,000 GPU, preferably at least about 9,000 GPU at about50% relative humidity in the temperature range of about 25° C. to about50° C. and/or the AA (or other VOCs) crossover of sulfonatedpolyaryletherketone/cellulose derivative coated membranes is less thanabout 1% at about 50% relative humidity at about 25° C., preferably lessthan about 3% at about 70% relative humidity at about 25° C., morepreferably less than about 1% at about 70% relative humidity at about25° C. and less than about 10% at about 90% relative humidity at about25° C., preferably less than about 6% at about 90% relative humidity atabout 25° C., more preferably less than about 3% at about 90% relativehumidity at about 25° C. The selectivity of water vapor over AA or otherVOCs is greater than about 100 at about 30% relative humidity at about25° C., greater than about 50 at about 50% relative humidity at about25° C., greater than about 20 at about 70% relative humidity at 25° C.,and greater than about 5 at about 90% relative humidity at about 25° C.

The water vapor transport, permeance, and permeability and/or theselectivity of the membrane may be affected by one or more oftemperature, humidity, and selective layer thickness. For suchmembranes, at a given temperature higher humidity may increase watervapor permeability and lower humidity may decrease water vaporpermeability. Temperature may affect the permeability of a membrane bychanging the rate of diffusivity through the membrane or the sorption ofwater vapor or other chemical species into the membrane. Relativehumidity, vapor pressure, or chemical potential of water in the membranemay affect one or more of the permeability of the membrane to chemicalspecies and/or the selectivity of the membrane. In some embodiments whenthe temperature is about 25° C., and/or the RH is about 50%, and/or thethickness of the selective layer is about 0.5 microns to about 2microns, preferably about 0.75 microns to about 1.25 microns, thepermeance of sulfonated polyaryletherketone/cellulose derivative coatedmembranes is at least about 6,000 GPU to greater than about 15,000 GPU,and/or the selectivity of the membrane for water vapor over AA ofsulfonated polyaryletherketone/cellulose derivative coated membranes isgreater than about 20, preferably greater than 50, and/or the aceticacid (AA) crossover is less than about 1%. At about 70% relativehumidity the AA selectivity is greater than about 20 and the AAcrossover is preferably less than about 3%.

By appropriately selecting the polymer blend of the selective layer onemay alter the functional relationship between water vapor permeabilityand/or selectivity and temperature and/or RH.

As described elsewhere herein, compared to sPEEK coated membranes,membranes coated with a blend of sPEEK and CA demonstrate improved highhumidity selectivity (measured as a lower acetic acid crossover (AAcrossover) at about 90% RH) and comparable WVT. Further, as describedelsewhere herein, compared to sPEEK coated membranes at the samethickness of selective layer 14 on substrate 12, sPEEK/CA membranesdemonstrate significant reductions in AA and ethanol crossover at higherhumidities (i.e. about 50% RH to about 90% RH).

In some embodiments when the temperature is about 25° C., and/or the RHis about 50%, and/or the thickness of the sPEEK/CA selective layer onsubstrate 12 is in the range of about 0.5 microns to about 2.5 microns,the water vapor permeance of sPEEK/CA coated membranes is in the rangeof about 6,000 GPU to about 15,000 GPU and/or the AA crossover ofsPEEK/CA coated membranes is in the range of about 0% to about 2%. Insome embodiments when the temperature is about 25° C., and/or the RH isabout 90%, and/or the thickness of the sPEEK/CA selective layer onsubstrate 12 is in the range of about 0.5 microns to about 2.5 microns,the water vapor permeance of sPEEK/CA coated membranes is in the rangeof about 6,000 GPU to about 15,000 GPU and/or the AA crossover ofsPEEK/CA coated membranes is less than about 6%. Water vapor permeanceis similar for both sPEEK and CA membranes at about 25° C. and about 50°C., but selectivity of the sPEEK/CA membrane is improved relative to thesPEEK membranes at higher relative humidity conditions.

By appropriately selecting the polymer blend of the selective layer asdescribed elsewhere herein, the WVT rate (WVTR) increases when theselective layer is exposed to higher RH or to higher temperature at sameRH.

In any of the above embodiments, the sPEEK/CA selective layers maycomprise an sPEEK:CA (wt.:wt.) ratio in the range of about 1:9 to about9:1, preferably about 7:3 to about 2:3 or be formulated from an sPEEK/CAcoating solution or dispersion comprising an sPEEK:CA (wt.:wt.) ratio inthe range of about 1:9 to about 9:1, preferably with an sPEEK:CA(wt.:wt.) ratio in the range of about 2:3 to about 7:3, and/or a weightpercent of sPEEK and CA in the range of about 1 wt. % to about 10 wt. %,preferably about 5 wt. %, in an acetone/water solvent or anacetone/water/ethanol solvent, preferably comprising about 70/30 toabout 80/20 (wt./wt.) acetone/water or about 58/22/20 to about 65/25/10(wt./wt./wt.) acetone/water/ethanol.

Selective layer 14 may have any combination of the abovecharacteristics.

Selective Layer Coating Solution or Dispersion Formulation

Selective layer 14 can be applied directly to substrate 12 by a coatingrod, slot-die, or similar device. In rod coating thickness may becontrolled by the rod selection, solution viscosity, as well as thesolids content in the coating solution. In slot die coating, thethickness can be controlled by the slot size, the fluid pumping rate,and solution solids content. Suitable application methods includedip-coating, Mayer rod, blade over roller coating, direct gravure,offset gravure, kiss coating, slot die and spray-coating. The wet,coated substrate is then typically passed through a dryer or oven toremove excess solvent and cause the coating to adhere to the substratesurface. Drying may be achieved, for example, through heated air dryingby convection. Production of these membranes can be completed onroll-to-roll equipment in a continuous process, allowing for highvolume, low cost manufacturing.

Selective layer 14 may be prepared by applying a solution or dispersioncomprising a sulfonated polyaryletherketone/cellulose derivative tosubstrate 12 as a coating. The coating may be dried until it is mostlyfree of solvent wherein a sulfonated polyaryletherketone/cellulosederivative selective layer covers a surface of the substratecontinuously.

Solvent systems found to dissolve both sPEEK and CA include but are notlimited to acetone/water, THF, THF/water, NMP, NMP/water, DMF,DMF/water, DMSO, DMSO/water, preferably acetone/water,acetone/water/ethanol, or another ternary solvent system. Acetone/wateror acetone/water/ethanol may be used to achieve thin, defect-freesPEEK/CA selective layers on a substrate surface.

In some embodiments, sPEEK/CA coating solutions or dispersions maycomprise an sPEEK:CA (wt.:wt.) ratio in the range of about 7:3 to about2:3, and/or a weight percent of sPEEK and CA in the range of about 2.5wt. % to about 10 wt. %, preferably 5 wt. %, and/or an acetone/watersolvent, preferably comprising about 70/30 to about 80/20 (wt./wt.)acetone/water or acetone/water/ethanol solvent, preferably comprisingabout 58/22/20 to about 65/25/10 (wt./wt./wt.) acetone/water/ethanol oranother ternary solvent system.

Acetone/water solutions of sPEEK/CA have pH of about less than about 1.However, acidic pH degrades CA in solution by acid hydrolysis. Thisdegradation will continue even after the sPEEK/CA coating solution isdried due to the presence of acetic acid generated during hydrolysis ofthe CA. This degradation can have an effect on the water vapor transportperformance and lifetime of the membranes. To substantially eliminate CAdegradation, a cation form of sPEEK may be used, wherein the protons ofthe sPEEK sulfonic acid groups are exchanged for sodium ions, lithiumions, or other monovalent cations (such as potassium ions) or divalentcations (such as calcium ions or magnesium ions). Preferably, sodiumions are used. Degradation of CA in sPEEK/CA coating solutions andsPEEK/CA selective layers is substantially eliminated byneutralizing/exchanging sPEEK in this way. Further, the WVT propertiesof neutralized/exchanged-sPEEK/CA selective layers are substantiallymaintained.

In some embodiments, about 80% to about 100% of the sulfonic acid groupprotons of sPEEK may be exchanged for sodium, lithium, or anothercation. For example, the protons of the sulfonic acid groups of sPEEKmay be exchanged for sodium ions by adding NaHCO₃ or NaOH dropwise to anacetone/water solution of a blend of the sPEEK and cellulose derivativeuntil the pH of the solution is between about 5 to about 6. In someembodiments the exchange of protons for cations can be completed beforethe cellulose derivative polymer is added. Sodium salts other thanNaHCO₃ (such as Na₂CO₃) may be used for the ion exchange. Alternatively,sPEEK may be treated with excess NaOH solution (such as 0.1 M NaOH), inwhich the polymer is soaked in 0.1 M NaOH solution and rinsed withdeionized water until the pH of the wash solution is neutral (i.e. pH isabout 7), and the resulting Na-sPEEK washed with deionized water anddried. Exchange of protons can also be completed after coating thesubstrate with sPEEK/CA and drying. In this case, salts such as NaCl orKCl could be used as the cation source. Persons skilled in the art willrecognize that the sulfonic acid group protons of other sulfonatedpolyaryletherketons may be replaced with cations as described above forsPEEK.

Substrate

Substrate 12 provides most of the mechanical support and largelydetermines the handling characteristics of membrane 10. For ERVapplications, substrate 12 preferably has the mechanical propertiesrequired in order be formed into an ERV core and to be integrated intoan ERV system. These properties may include one or more of thefollowing: the ability to hold a pleat or fold; the ability to bethermo-formed; tear-resistant; sufficiently rigid to support itselfbetween ribs or other supports without undue deformation; and theability to be thermally-, vibration- or ultrasonically-welded. Theseproperties may be advantageous when handling, sealing, and/or bondingmembrane 10 and/or creating flow pathways from membrane 10 and/or onmembrane 10 surfaces when assembling an ERV core.

Substrate 12 may have a high porosity. In some embodiments, substrate 12has a porosity of at least about 30%, preferably in the range of about30% to about 80%) and/or is thin (e.g. has a thickness of less thanabout 250 microns) and/or is hydrophobic.

Higher porosity and lower thickness of the substrate helps decrease theresistance to water and water vapor transport (WVT) through thesubstrate portion of the membrane. High porosity and low thickness aredesired with the constraint that the substrate should provide sufficientmechanical strength to withstand expected handling without damage. Thepore size is preferably just small enough to allow a continuous coatingof polymer to be formed on the surface of the substrate.

In some embodiments the substrate has one or more of these features.Substrates of particular embodiments have a thickness that is <250microns, preferably in the range of about 4 microns to about 150microns, more preferably in the range of 5 to 40 microns.

In some embodiments the average pore size of the substrate is in therange of about 5 nm to about 1,000 nm in the width or length direction,preferably in the range of about 5 nm to about 500 nm in the width orlength direction.

Suitable substrates may comprise electro spun nanofibrous layers(supported on a macroporous substrate layer). Fibers may be electro spunfrom polymer solutions and deposited on a carrier layer (such as anon-woven). Sulfonated polyaryletherketone blend formulations can thenbe coated on or impregnated into the nanofibrous layer usingconventional coating methods (such as gravure or slot die coating). FIG.1B shows a membrane 110 according to an example embodiment. Membrane 110comprises an electro spun nanofibrous layer 115 supported on amacroporous substrate layer 112. A selective layer 114 is coated on asurface 113 of nanofibrous layer 115, and may impregnate the nanofibrouslayer. Membrane 110 is air impermeable and permeable to water vapor. Asdescribed elsewhere herein, selective layer 114 may comprise at leastone sulfonated polyaryletherketone blended with at least one cellulosederivative. Substrates comprising electro spun nanofibrous layers may beimpregnated or surface coated with sulfonated polyaryletherketoneblends, such as sPEEK blended with CA. An advantage of utilizingnanofibrous scaffolds as a basis for membrane fabrication is thatselective layer 114 can be coated on a wide variety of support layers,allowing for the creation of formable membrane materials.

Suitable substrates may be polymeric, such as a polyolefin (e.g.polyethylene (PE)) with desiccant or silica additives such as silica orvarious inorganic fillers (e.g. oxides of silicon, titanium, aluminum).In some embodiments the substrates comprise uni-axially or bi-axiallystretched polyolefins such as polyethylene (PE) or polypropylene (PP).These porous polyolefins can be supplied as multilayer laminates ofsingle polymers (PE or PP) or of multiple polymers (PP/PE/PP, etc.) oras individual films of different thicknesses. Other suitable substratesinclude expanded polytetrafluoroethylene (PTFE), UHMWPE fibrous poroussubstrates or other filler-loaded polymer films.

Suitable substrates may be made from a microporous polyolefin material.In some embodiments the microporous polyolefin substrate may be producedby a dry-process or a wet-process. For example, in some embodiments thesubstrate comprises a dry-process polypropylene (DP-PP) batteryseparator. Such separators are used, for example, in some lithium ionbatteries. Such separators are commercially available and are reasonablyinexpensive in commercial volumes.

In wet-process fabricated substrates, a plasticizer-loaded polyolefinfilm is extruded as a gel. The plasticizer is then extracted with asolvent leaving a polyolefin skeleton film with an open pore structure.The pore structure of the polyolefin can then be further modified bystretching. In a dry-process, the polyolefin is extruded as a melt,aligning the polymer lamellae; this polymer film is then annealed, andthen stretched orthogonally to the aligned direction to inducecontrolled tearing of the polymer structure, leading to a microporousstructure (see, for example, S. S. Zhang, “A review on the separators ofliquid electrolyte Li-ion batteries,” Journal of Power Sources, vol.164, no. 1, pp. 351-364, January 2007 and P. Arora and Z. (John) Zhang,“Battery Separators,” Chem. Rev., vol. 104, no. 10, pp. 4419-4462,October 2004).

If the substrate is made of a highly porous material with a large poresize, the coating making up selective layer 14 will tend to penetratethe pores prior to drying, leading to partial or full impregnation ofthe substrate. This is not desirable since an impregnated substrate willtend to have a greater resistance to water transport than a membranecomprising a thin surface coating of a selective polymer. Penetration ofthe polymer into the substrate occurs more readily in substrates thatare fibrous in nature. Such substrates tend to ‘wick in’ polymer coatingsolutions or dispersions, and have less defined surface pore structures.More fibrous substrates also tend to have greater pore sizedistributions and larger average pore sizes, leading to more penetrationof the polymer into the substrate. Thus, the substrate preferably hashigh porosity but a small pore size, a narrow pore size distribution,and a well-defined surface pore structure to facilitate coatingselective layer 14 onto the substrate with little or no impregnationinto the pores of the substrate

Polyolefin substrates made using a wet-process tend to have a greaterpore size distribution and often a greater average pore size. Thus, thecoating making up selective layer 14 will tend to penetrate the pores ofwet-process polyolefin substrates, leading to a polymer-impregnatedsubstrate. Such membranes tend to have a thicker selective layer andlower WVT performance.

In contrast, microporous polyolefin substrates produced using adry-process tend to have a more definite surface pore structure, with anarrower pore size distribution, and may be coated with little or noimpregnation of the polymer into the substrate. Rather cross-sectionalscanning electron microscopy (SEM) images show that a well-definedcoating layer remains at the surface of dry-process substrates. The useof dry-process substrates has been found to allow for fabrication ofmembranes comprising selective layers with a lower effective thicknessthan when the same coatings are cast on wet-process substrates, whichallows for higher WVT performance.

Further, polyolefin substrates made using a dry-process tend to havehigher humidity selectivity than wet-process polyolefin substrates. Forexample, as described elsewhere herein, membranes comprising DP-PPsubstrates have high humidity selectivity (measured as a low acetic acidcrossover (AA crossover) at a relative humidity (RH) of about 90%)relative to membranes comprising WP-PE substrates or silica polyethylene(Si-PE) substrates.

Suitable substrates may comprise non-polymeric microporous materials(e.g. glass-fiber based materials). As described elsewhere herein,selective layer 14 may comprise at least one sulfonatedpolyaryletherketone with at least one cellulose derivative.Non-polymeric microporous substrates may be impregnated or surfacecoated with sulfonated polyaryletherketone blends to give membranes withdesirable properties for some applications. In some embodimentsfree-standing films of the sPEEK blends can be cast and laminated on toa support layer.

Suitable substrates may comprise laminated layers for improving thehandling properties of thin substrates. For example, a mechanicalsupport layer such as a non-woven (for example, spun-bond, melt blown,spun-melt-spun (SMS), which has a low basis weight (<100 g/m²,preferably <35 g/m²) and high porosity, may be laminated (for example,by heat or adhesive) with the substrates described elsewhere herein.

Substrate 12 is preferably inherently flame retardant (i.e. made of oneor more flame retardant materials) and/or tends to shrink away fromhigh-temperature sources such as open flames. These properties helpmembrane 10 to pass flammability testing (e.g. according to UL-94,UL-723). Since the substrate tends to constitute the major portion byweight of the final membrane, if the substrate is flame retardant, thenit can be expected that the membrane itself will also be flameretardant.

In some embodiments substrate 12 does not promote and/or is resistant tomicrobial growth.

Substrate 12 may have any combination of the above characteristics.

Additives

The properties of membrane 10 can be further enhanced for the particularend-use application by incorporating additives into the selective layer,as described in U.S. patent application Ser. No. 13/321,016 (publishedas US 2012/0061045) which is hereby incorporated by reference in itsentirety. Additives include, but are not limited to, flame retardants,desiccants, zeolites, inorganic additives (such as silica, titania, andalumina), plasticizers, surfactants, desiccant salts, and microbicides.

Method of Manufacture

FIG. 2 illustrates a method 20 for making a membrane. In block 21 asuitable substrate is provided. The substrate may, for example, be asdescribed above. In some embodiments the substrate is a dry- orwet-process polypropylene or polyethylene substrate. In optional block22 the substrate is prepared to receive the selective layer 14. Block 22may, for example, comprise corona treatment of the substrate.

In block 23 a solution or dispersion is prepared for use in creating theselective layer. The solution or dispersion contains at least onesulfonated polyaryletherketone polymer (such as sPEEK) blended with atleast one cellulose derivative (such as CA) and optionally containsother additives as described elsewhere herein.

In example embodiments the weight percent of the sulfonatedpolyaryletherketone polymer/cellulose derivative making up the solutionor dispersion used in forming the selective layer is in the range ofabout 1 wt. % to about 10 wt. %, preferably about 5 wt. %. Usingsolutions or dispersions with a lower weight percent of sulfonatedpolyaryletherketone polymer/cellulose derivative yield thinner coatinglayers.

In block 24 the solution or dispersion prepared in block 23 is appliedto the substrate to create the selective layer. Without being limited toa specific method, application may for example comprise gravure coating,meter rod coating, roll coating, slot die coating or spray coating. Slotdie coating is preferred to provide thin uniform coatings on thesubstrate surface.

In block 25 the selective layer is dried (i.e. physically cured). Afterdrying, a continuous dense film layer of sulfonated polyaryletherketonepolymer/cellulose derivative covers the substrate surface. The denselayer is substantially free of pores. In some embodiments the thicknessof the selective layer is in the range of about 0.1 to about 10 microns(for example, a coating weight of about 0.1 to about 10 g/m²).

The selective layer may be dried in air. In some embodiments the coatedsubstrate may be dried in air at a temperature of about 20° C. to about90° C. Drying may be expedited by heating the coated substrate. Forexample, in other embodiments drying occurs in a roll-to-roll process ina heated convection oven. In such embodiments, drying of the selectivelayer may be completed in a time on the order of 30 seconds or less.

In a method according to an example embodiment, a membrane 10 isprepared by applying a film comprising an sPEEK/CA dispersion to a DP-PPsubstrate 12. The film is allowed to dry. The sPEEK/CA selective layercovers a surface of the substrate continuously.

Pore Formation on Phase Inversion

In the present process, depending on conditions, once the selectivelayer coating solution/dispersion is applied to substrate 12, thesolvent may begin to evaporate rapidly. Solvents with higher vaporpressure may evaporate faster than higher boiling solvents. Since theselective layer comprises a blend of two polymers with varying levels ofsolubility in the chosen solvent, there is a possibility for ‘phaseinversion’ in the selective layer. For example, phase inversion mayoccur in acetone-water solutions of sPEEK/CA due to the rapidevaporation of acetone and the insolubility of CA in water.

Phase inversion occurs as polymer rich and polymer lean phases developin the coating layer during drying. For example, in an acetone/water/CAsystem, CA is more soluble in acetone (solvent) than water (non-solvent)and acetone evaporates at a higher rate than water from the coatinglayer. During drying the coating layer separates into polymer rich andpolymer lean phases, the polymer rich phase solidifying before thepolymer lean phase and the polymer lean phase forming pores in thepolymer rich phase. When completely dried, pores remain throughout thefilm layer. In an acetone/water/sPEEK/CA system, sPEEK is more solublein lower acetone/water ratios than CA. During drying, as acetoneevaporates sPEEK remains in solution longer and pores are therefore lesslikely to form when sufficient sPEEK is present.

Pore formation by phase inversion is generally undesirable in preparingmembrane 10. Porous phase inversion membranes and layers tend to befragile, brittle, and prone to fracture and failure when compressed,bent, folded, or handled due to their pore structure and high number ofinterphases making handling membrane and/or pleating the membrane intoexchanger modules problematic.

Further, selective layer 14 should be dense (i.e. substantially free ofvoids) and non-porous in order to provide selective transport of watervapor over other gases and VOCs. In contrast, phase inversion membranestend to be porous. Phase inversion may be reduced or avoided bymodifying one or more of the following: the solvent ratios, the polymersolids content, the polymer ratios, the drying rate, and/or the filmthickness. For example, pore formation by phase inversion is greaterwhen the solids content of the coating is lower.

Adding other solvents and/or non-solvents to the system may also impactpore formation by phase inversion. For example, CA is not soluble inethanol or water, but ethanol is a more volatile non-solvent than water.By adding ethanol to a acetone/water/sPEEK/CA system, pore formation byphase inversion is reduced. For example, when the total wt. % of ethanolin the system is greater than about 10 wt. %, preferably greater thanabout 15 wt. %, pore formation by phase in version was observed todecrease.

No significant pores were observed resulting from phase inversion formembranes comprising an sPEEK/CA selective layer wherein the sPEEK:CAratio is in the range of about 2:3 to about 1:0 (solids content of thecoating solution in the range of about 4 wt. % to about 10 wt. % inabout 70/30 to about 80/20 (wt./wt.) acetone/water) for selective layersup to 2 microns in thickness on a microporous DP-PP substrate. Nosignificant pores were observed resulting from phase inversion forsPEEK/CA films wherein the sPEEK:CA ratio is in the range of about 2:3to about 1:0 (case from an acetone/water system). In contrast, poreswere clearly observed in the surface and throughout sPEEK/CA filmshaving sPEEK:CA ratios less than 1:2 (for example, 1:3) due to phaseinversion when cast from acetone/water systems. FIGS. 3 and 4 showsurface and cross-section images, respectively, of an unsupportedsPEEK/CA film cast from 80/20 (wt./wt.) acetone/water wherein thesPEEK:CA ratio was 1:2. Complex pore structures in the surface andthroughout the sPEEK/CA films were also clearly observed in membranescomprising an sPEEK/CA selective layer wherein the solids contentformulation of the selective layer was less than about 3% in 80/20(wt./wt.) acetone/water. FIG. 5 shows an electron microscopy (EM) imageof the surface of a membrane comprising an sPEEK/CA selective layer caston DP-PP and having an sPEEK:CA ratio of 1:1 (cast from a 2.5% solidscontent formulation in 80/20 (wt./wt.) acetone/water). The porestructure observed is believed to have been created by phase inversion.Simple bending, folding, and pleating tests caused such phase inversioninduced porous membranes to crack, leading to increased air crossover.Membranes having a ‘glossy’ film layer surface showed no surface orthrough porosity, or evidence of pores formed by phase inversion, underEM. These membranes could be bent, folded, and pleated withoutdemonstrating an increase in air crossover.

Polymer-Polymer Phase Separation in Films

Polymer blends, particularly those that are incompatible and cannotcompletely intersperse on the molecular level may tend tothermodynamically separate into ‘phase separated’ solids regionscontaining the individual polymer components to reduce or minimize freeenergy in the film layer. This may happen during drying/solventevaporation and/or during thermal treatment. These non-porous phaseseparated film layers can have positive and negative effects on the bulkperformance properties of the film.

In selective layer 14, some degree of polymer-polymer phase separationof sPEEK/CA selective layers is often desirable. For example, regions ofCA (which have lower swelling in the presence of water) may constrainhigher swelling sPEEK regions, prevent excess dimensional instability ofthe selective layer in the presence of higher RH, and decreasepermeability of the selective layer to VOCs and other gases in thepresence of high RH. When pore formation is substantially avoided,polymer-polymer phase separation may also be beneficial for preventingmechanical failure of the selective layer due to extreme swelling andcontracting of sPEEK under varying RH conditions and in the presence ofliquid water condensation. Further, defined regions of sPEEK (which havehigher water vapor permeability) may allow higher localized WVT (i.e.more defined regions of the polymer containing sulfonic acid groups mayimprove water vapor transport).

Blending polymers in different ratios will lead to different levels ormorphologies of phase separation. Membranes comprising sPEEK/CAselective layers formulated from an sPEEK/CA coating solution having ansPEEK:CA (wt.:wt.) ratio in the range of about 7:3 to about 2:3demonstrate polymer-polymer phase separation of sPEEK and CA withoutpore formation (FIGS. 6-9). FIG. 6 shows a 2:1 (wt.:wt) sPEEK:CA filmsurface having polymer-polymer phase separation induced morphology. Nopores are seen in the film surface. FIG. 7 shows a DP-PP substratecoated with about a 1 micron film of a 1:1 (wt.:wt.) sPEEK:CA coatingsolution (5 wt. % polymer solids in a 72/28 acetone/water solution). Thecoating morphology suggests that distinct polymer phases were formed,but no pores. FIGS. 8 and 9 show cross-sections of films cast from 1:1(wt.:wt.) sPEEK:CA and 2:3 (wt.:wt) sPEEK:CA formulations, respectively,cast from acetone/water. These films did not demonstrate phase inversioninduced pores (as observed for the 1:2 (wt.:wt.) sPEEK:CA film shown inFIG. 4); however, polymer-polymer phase separation is observable in thefilm morphology shown in FIGS. 8 and 9. Phase inversion (i.e. poreformation) was not observed for membranes comprising sPEEK:CA selectivelayers formulated from an sPEEK/CA coating solution having an sPEEK:CA(wt.:wt.) ratio in the range of about 7:3 to about 2:3 (greater thanabout 3 wt. % solids content in acetone/water), but polymer-polymerphase separation was visible in the film morphology.

The invention is illustrated by the following non-limiting examples.

Example 1—Sulfonation of PEEK

Seven samples of sulfonated PEEK with different degrees of sulfonationwhere prepared by sulfonating PEEK from Victrex® (MW 34,000).Sulfonation was performed according to the procedure described in N.Shibuya and R. S. Porter, “Kinetics of PEEK sulfonation in concentratedsulfuric acid,” Macromolecules, vol. 25, no. 24, pp. 6495-6499, November1992 by dissolving 30 g of PEEK in 500 mL of sulfuric acid (95-98 wt. %,Sigma Aldrich). Seven such solutions were vigorously stirred at roomtemperature for 96, 120, 144, 172, 192, 264, and 336 h, respectively.After completion of the reaction time, the mixture was precipitated inwater and washed until pH >5. The sulfonated polymer was dried in a 50°C. oven for at least 24 h. The corresponding ion exchange capacity (IEC)and degree of sulfonation (DS) were determined by titration as describedin M. H. D. Othman, A. F. Ismail, and A. Mustafa, Malaysian PolymerJournal, 2007, 2, 10-28. The results are shown in Table 1.

TABLE 1 Sulfonation Ion exchange Degree of reaction capacity sulfonationEstimated time (h) (meq/g) (%) MW 96 0.73 22.7 36.107 120 0.77 24.236.243 144 1.00 32.3 36.978 172 1.48 50.2 38.602 192 1.81 63.9 39.845216 2.26 84.8 41.741 336 2.38 90.4 42.249

The DS ranged from about 23% to about 90% depending on the reactiontime. For formulating and coating considerations, as well as swellingand performance considerations, a DS in the range from about 60% toabout 70% was generally found to be preferred for the WVT applicationsdescribed herein.

Example 2—Preparation and Testing of Membranes with a Si-PE SubstrateCoated with Various Blends of sPEEK and CA

A silica polyethylene (Si-PE) composite material (silica-loadedpolyethylene substrate SP400 from PPG) was used as a microporoussubstrate, and eleven supported membrane samples were prepared bycoating the substrate with sPEEK (DS 63%) or CA (39.7% acetyl content,average M_(N) ca. 50,000) or blends thereof. The properties of theresulting membranes were tested to determine the effect of increasingthe proportion of CA in the blended polymer. Sample 2A was coated withsPEEK only, and was prepared by applying a thin coating of an sPEEKsolution (1 g of sPEEK in acetone/water, 10% solids) to one surface ofthe Si-PE substrate using a Mayer rod coater (the coating process usedin all the Examples is described in further detail herein). Sample 2Kwas coated with CA only, and was prepared by applying a thin coating ofa CA solution (1 g of CA in acetone/water, 10% solids) to one surface ofthe Si-PE substrate using a Mayer rod coater. In Samples 2B-2J, thesubstrate was coated with a blend of sPEEK and CA; the percentage byweight of CA in the polymer blend was increased in 10% incrementsthrough Samples 2B -2J. The membrane preparation method was essentiallythe same for all Samples 2A-2K, and the % solids in the acetone/watersolution was 10% in each case. For example, for Sample 2F, 0.5 g of CAand 0.5 g of sPEEK (DS 63%) in acetone/water (10% solids, 5% CA, 5%sPEEK) was mixed together at room temperature until a clear solution wasobtained. A thin coating of the CA/sPEEK solution was applied to onesurface of Si-PE substrate using a Mayer rod coater. For each membranesample the coating loading was determined, and the membrane was testedfor air crossover, exhaust air transport ratio (EATR), water permeation(WVTR), and acetic acid permeation (AA crossover), using techniquesdescribed herein. The results are shown in Table 2.

TABLE 2 (Si-PE substrate) EATR EATR AA cross- AA cross- sPEEK/CA Coating2000 500 WVTR over (%) over (%) Membrane ratio by loading cc cckg/m²/day at RH at RH Sample # weight * g/m² (%) (%) (50° C.)** 0% 90%2A 100/0  2.56 0 0 25.3 0.2 12.3 2B 90/10 2.82 0 0 24.6 0.3 9.8 2C 80/202.89 0 0 26.4 0.2 10.1 2D 70/30 3.21 0 0 26.6 0.1 9.7 2E 60/40 2.98 0 023.6 0.1 9.4 2F 50/50 2.85 0 0 25.7 0.1 10.5 2G 40/60 3.17 0 0 25.9 0.39.8 2H 30/70 3.38 0 0 22.9 0.2 10.1 2I 20/80 2.91 0 0 21.7 0.1 9.7 2J10/90 3.39 0 0 19.6 0.1 9.4 2K  0/100 2.57 0.5 1.4 22.4 0.4 n/a * fromacetone/water (8/2) solution, 10% solids **dynamic WVT test, 33 cm²area, 6,000 cm³/min flow, 50% RH in feed n/a indicates not measured

The air crossover was zero for all Samples 2A-K indicating that thecoating formed a continuous layer or dense film on the substrate. TheEATR was zero for all membrane samples, except Sample 2K which wascoated with CA alone and had defects in it. Even though the WVTR of themembrane with 100% CA coating was lower than the membrane with 100%sPEEK coating at a similar loading (22.4 versus 25.3 kg/m²/day), it canbe seen that adding CA to the coating did not adversely affect the WVTReven up to about 60% by weight CA in the blend. As shown in Table 2, AAcrossover was low for all of the coated membrane samples at dryconditions (RH 0%). However, the AA crossover was significantlyincreased at high humidity conditions (RH 90%). Without being bound byany theory, this is believed to be due to plasticization of the membranecoating polymer by water vapor. These Si-PE based membrane samples didnot pass the UL-94HB (horizontal burn) flame test described herein.

Example 3—Preparation and Testing of Membranes with a WP-PE SubstrateCoated with Various Blends of sPEEK and CA

This example is similar to Example 2 except that WP-PE was used as thesubstrate. Eleven supported membrane samples were prepared by coatingthe WP-PE substrate with sPEEK (DS 63%) or CA (39.7% acetyl content,average M_(N) ca. 50,000) or blends thereof, and properties of theresulting membranes were tested to determine the effect of increasingthe proportion of CA in the blended polymer. Sample 3A was coated withsPEEK only, and was prepared by applying a thin coating of an sPEEKsolution (1 g of sPEEK in acetone/water, 10% solids) to one surface ofthe substrate using a Mayer rod coater. Sample 3K was coated with CAonly, and was prepared by applying a thin coating of a CA solution (1 gof CA in acetone/water, 10% solids) to one surface of the substrateusing a Mayer rod coater. In Samples 3B-3J the substrate was coated witha blend of sPEEK and CA; the percentage by weight of CA in the polymerblend was increased in 10% increments through Samples 2B -2J. Themembrane preparation method was essentially the same for all Samples2A-2K, and the % solids in the acetone/water solution was 10% in eachcase. For example, for Sample 3F, 0.5 g of CA and 0.5 g of sPEEK (DS63%) in acetone/water (10% solids, 5% CA, 5% sPEEK) was mixed togetherat room temperature until a clear solution was obtained. A thin coatingof the CA/sPEEK solution was applied to one surface of the WP-PEsubstrate using a Mayer rod coater. For each membrane sample the coatingloading was determined, and the membrane was tested for air crossover,exhaust air transport ratio (EATR), water permeation (WVTR), and aceticacid permeation (AA crossover), using techniques described herein. Theresults are shown in Table 3.

TABLE 3 (WP-PE substrate) EATR EATR AA cross- AA cross- sPEEK/CA Coating2000 500 WVTR over (%) over (%) Membrane ratio by loading cc cckg/m²/day at RH at RH Sample # weight * g/m² (%) (%) (50° C.)** 0% 90%3A 100/0  1.59 0 0 30.2 0.2 11.1 3B 90/10 1.81 0 0 29.7 0.3 10.5 3C80/20 1.89 0 0 31.5 0.2 11.8 3D 70/30 1.81 0 0 28.8 0.1 10.2 3E 60/401.74 0 0 30.6 0.1 12.1 3F 50/50 1.77 0 0 31.4 0.1 11.3 3G 40/60 2.03 0 026.7 0.1 6.1 3H 30/70 2.04 0 0 26.2 0.1 6.6 3I 20/80 1.95 0 0 25.0 0.16.3 3J 10/90 1.80 0 0 24.0 0.1 6.3 3K  0/100 2.68 0 0 16.5 0.1 n/a *from acetone/water solution, 10% solids **dynamic WVT test, 33 cm² area,6,000 cm³/min flow, 50% RH in fee n/a indicates not measured

The air crossover and EATR was zero for all Samples 2A-K indicating thatthe coating formed a continuous layer or dense film on the substrate.Even though the WVTR of the membrane with 100% CA coating was lower thanthe membrane with 100% sPEEK coating (16.5 versus 30.2 kg/m²/day), itcan be seen that adding CA to the coating did not adversely affect theWVTR even up to about 60% by weight CA in the blend. In fact,surprisingly it appears that the WVTR was higher for some of the blendsthan for sPEEK alone, even when the coating loading was higher (e.g.Samples 3C, 3E and 3F). The crossover of acetic acid (AA) wassignificantly increased at high humidity conditions (RH 90%), againlikely due to plasticization of the membrane coating polymer by watervapor. However, this effect was lower for some of the membranes withblended coatings (3G-J). This effect of improved high humidityselectivity is even more prominent for a DP-PP substrate having a thinmembrane coating polymer (see Example 10 herein). These WP-PP basedmembrane samples also passed UL-94HB (horizontal burn) flame testdescribed herein.

Example 4—Preparation and Testing of Membranes with a WP-PE SubstrateCoated with Various Blends of sPEEK and CA at Various Solids Contents

In this example, the percentage solids in the coating solution wasvaried. Four supported membrane samples were prepared as in Example 3 bycoating a WP-PE substrate with a 50/50 by weight blend of sPEEK (DS 63%)and CA (39.7% acetyl content, average M_(N) ca. 50,000) in acetone/watersolution. For Sample 4A the solution was 8% solids (0.4 g sPEEK, 0.4 gCA), for Sample 4B the solution was 7% solids (0.35 g sPEEK, 0.35 g CA),for Sample 4C the solution was 6% solids (0.3 g sPEEK, 0.3 g CA), andfor Sample 4D the solution was 5% solids (0.25 g sPEEK, 0.25 g CA). Theproperties of the resulting membranes were tested to determine theeffect of changing the solids content in the coating solution. For eachmembrane sample the coating loading was determined, and the membrane wastested for air crossover, exhaust air transport ratio (EATR), waterpermeation (WVTR), and acetic acid permeation (AA crossover), usingtechniques described herein. The results are shown in Table 4, and arecompared with the results of Example 3 Sample 3F where the solidscontent was 10%.

TABLE 4 (WP-PE substrate) EATR EATR AA cross- AA cross- Coating 2000 500WVTR over (%) over (%) Membrane sPEEK/CA loading cc cc kg/m²/day at RHat RH Sample # % solids * g/m² (%) (%) (50° C.)** 0% 90% 3F 10%  1.77 00 31.4 0.1 11.3 4A 8% 1.59 0 0 32.0 n/a n/a 4B 7% 1.28 0 0 31.6 n/a n/a4C 6% 1.24 0 0 32.4 n/a 10.2 4D 5% 1.10 0 0 34.9 0.1  8.39 * 50/50 byweight of sPEEK/CA in acetone/water solution **dynamic WVT test, 33 cm²area, 6,000 cm³/min flow, 50% RH in feed n/a indicates not measured

The air crossover was zero for each of the Samples 4A-D. As thepercentage solids content was reduced, the coating loading tended todecrease, causing an increase in WVTR. However, it appears thatdecreasing the coating weight (and thickness) does not cause anyincrease in the crossover of acetic acid.

Example 5—Preparation and Testing of Membranes with a WP-PE SubstrateCoated with Various Blends of sPEEK and CAP

This example is similar to Example 3 except that cellulose acetatepropionate (CAP) (average M_(N) ca. 25,000 by GPC, ca. 2.5% acetylcontent, ca. 2.6 wt. % hydroxyl, ca. 45 wt. % propionyl from SigmaAldrich was used in the polymer coating blends instead of CA. Foursupported membrane samples were prepared by coating the WP-PE substratewith CAP or blends of CAP with sPEEK (DS 63%), and properties of theresulting membranes were tested to determine the effect of increasingthe proportion of CAP in the blended polymer. Sample 5A was prepared byattempting to apply a thin coating of an sPEEK/CAP solution (0.5 g ofsPEEK and 0.5 g CAP in 9/1 acetone/water, 10% solids) to one surface ofthe substrate using a Mayer rod coater; however the blend separated astwo phases and could not be used as a coating with this solvent system.Sample 5B was prepared by similarly applying a thin coating of ansPEEK/CAP solution (0.3 g of sPEEK and 0.7 g CAP in acetone/water, 10%solids). Sample 5C was prepared by similarly applying a thin coating ofan sPEEK/CAP solution (0.2 g of sPEEK and 0.8 g CAP in acetone/water,10% solids). Sample 5D was prepared by similarly applying a thin coatingof a CAP solution (1 g of CAP in acetone/water, 10% solids). For eachmembrane sample the coating loading was determined, and the membrane wastested for air crossover, exhaust air transport ratio (EATR), waterpermeation (WVTR), using techniques described herein. Acetic acidpermeation (AA crossover) was not tested as the membranes all haddefects. The results are shown in Table 5, and are compared with theresults of Example 3 Sample 3A where the coating was 100% sPEEK.

TABLE 5 (WP-PE substrate) sPEEK/ Air EATR EATR CAP Coating cross- 2000500 WVTR Membrane ratio by loading over cc cc kg/m²/day Sample #weight * g/m² (cc/min) (%) (%) (50° C.)** 3A 100/0  1.59 0 0 0 30.2 5A50/50 n/a n/a n/a n/a n/a 5B 30/70 1.95 4 1 4.8 19.0 5C 20/80 2.32 2 0.53.8 17.3 5D  0/100 1.65 0 0 0.5 16.3 * in acetone/water solution**dynamic WVT test, 33 cm² area, 6,000 cm³/min flow, 50% RH in feed n/a:for Sample 5A the blend separated as two phases and could not be used asa coating with this solvent system.

There was difficulty creating blend solutions and blend membranes withthe CAP/sPEEK polymers. The membranes that had sufficiently low defectsto test, had much lower WVTR than sPEEK coatings alone, showing thatblends of sPEEK and CAP did not perform as well as blends of sPEEK andCA. This indicates that adding CAP adversely affected the membraneproperties, unlike adding CA.

Example 6—Preparation and Testing of Membranes with a WP-PE SubstrateCoated with Various Blends of sPEEK and CAB

This example is similar to Examples 3 and 5 except that celluloseacetate butyrate (CAB) was used in the polymer coating blends instead ofCA or CAP. Six supported membrane samples were prepared by coating theWP-PE substrate with CAB (average M_(N) ca. 70,000 by GPC, 12-15% acetylcontent, 1.2-2.2 wt. % hydroxyl, 35-39 wt. % propionyl, from SigmaAldrich) or blends of CAB with sPEEK (DS 63%), and properties of theresulting membranes were tested to determine the effect of increasingthe proportion of CAB in the blended polymer. Sample 6A was prepared byattempting to apply a thin coating of an sPEEK/CAB solution (0.9 g ofsPEEK and 0.1 g CAB in 9/1 acetone/water, 10% solids) to one surface ofthe substrate using a Mayer rod coater. Sample 6B was prepared byattempting to apply a thin coating of an sPEEK/CAB solution (0.7 g ofsPEEK and 0.3 g CAP in acetone/water, 10% solids). Sample 6C wasprepared by attempting to apply a thin coating of an sPEEK/CAB solution(0.5 g of sPEEK and 0.5 g CAB in acetone/water, 10% solids). In allthree cases (Samples 6A, 6B and 6C) the blend separated as two phasesand could not be used as a coating with this solvent system. Sample 6Dwas prepared by applying a thin coating of an sPEEK/CAB solution (0.3 gof sPEEK and 0.7 g CAB in acetone/water, 10% solids). Sample 6E wasprepared by applying a thin coating of an sPEEK/CAB solution (0.2 g ofsPEEK and 0.8 g CAB in acetone/water, 10% solids). Sample 6F wasprepared by applying a thin coating of a CAB solution (1 g of CAB inacetone/water, 10% solids). For each membrane sample the coating loadingwas determined, and the membrane was tested for air crossover, exhaustair transport ratio (EATR), water permeation (WVTR), using techniquesdescribed herein. Acetic acid permeation (AA crossover) was not testedas the membranes all had defects. The results are shown in Table 6, andare compared with the results of Example 3 Sample 3A where the coatingwas 100% sPEEK.

TABLE 6 (WP-PE substrate) sPEEK/ Air EATR EATR CAB Coating cross- 2000500 WVTR Membrane ratio by loading over cc cc kg/m²/day Sample #weight * g/m² (cc/min) (%) (%) (50° C.)** 3A 100/0  1.59 0 0 0 30.2 6A90/10 n/a n/a n/a n/a n/a 6B 70/30 n/a n/a n/a n/a n/a 6C 50/50 n/a n/an/a n/a n/a 6D 30/70 2.05 11  2.9 8.7 12.3 6E 20/80 2.21 8 2.4 7.7 14.16F  0/100 1.51 0 0 0 10.6 * in acetone/water solution **dynamic WVTtest, 33 cm² area, 6,000 cm³/min flow, 50% RH in feed n/a: the blendsseparated as two phases and could not be used as coatings with thissolvent system.

Similar to the blends of sPEEK and CAP, the WVTR performance wassignificantly adversely affected by the presence of the CAB polymer inthe coating. The CAB also had compatibility problems in that it wasimmiscible with the sPEEK polymer in acetone/water formulations.

Example 7—Preparation and Testing of Membranes with a WP-PE SubstrateCoated with a Blend of sPEEK and EC

This example is similar to Examples 3, 5, and 6 except that ethylcellulose (EC) was used in the polymer coating blends instead of CA,CAP, or CAB. Four supported membrane samples were prepared by coatingthe WP-PE substrate with EC (48.0-49.5% (w/w) ethoxyl basis, from SigmaAldrich) at three different solids contents for the coating solution,and for a 50/50 blend of EC with sPEEK (DS 85%), and properties of theresulting membranes were tested to determine the effect of adding EC tothe sPEEK as a blended polymer. Since EC is insoluble in acetone/water,sPEEK with DS 85% was used for solubility purposes in ethanol/water.Sample 7A was prepared by applying a thin coating of an sPEEK/ECsolution (0.5 g of sPEEK and 0.5 g EC in 9/1 ethanol/water, 10% solids)to one surface of the substrate using a Mayer rod coater. Samples 7B-Dwere prepared by similarly applying a thin coating of an EC solution inethanol at 10%, 7%, and 5% solids contents respectively. For eachmembrane sample the coating loading was determined, and the membrane wastested for air crossover, exhaust air transport ratio (EATR), waterpermeation (WVTR), using techniques described herein. The results areshown in Table 7, and are compared with the results of Example 3 Sample3A where the coating was 100% sPEEK (DS 63%).

TABLE 7 (WP-PE substrate) Air EATR EATR sPEEK/EC Coating cross- 2000 500WVTR Membrane ratio by % loading over cc cc kg/m²/day Sample # weightsolids g/m² (cc/min) (%) (%) (50° C.)**** 3A 100/0*    10% 1.59 0 0 030.2 7A 50/50**   10% 1.52 0 0 0 20.3 7B 0/100*** 10% 2.11 0 0 0 18.2 7C0/100***  7% 1.96 0 0 0 25.6 7D 0/100***  5% 0.72 0 0.5 1 27.3 *in 80/20(wt.:wt.) acetone/water solution **in 90/10 (wt.:wt.) ethanol/watersolution ***in pure ethanol solution ****dynamic WVT test, 33 cm² area,6,000 cm³/min flow, 50% RH in feed

The water transport properties of the membranes comprising a blend ofsPEEK and EC were not improved when compared with membranes comprisingsPEEK or EC coatings. Reducing the solids content of the EC solutionresulted in reduced coating loadings and a corresponding increase inwater transport. Sample 7D had defects, hence the EATR results.

Example 8—Preparation and Testing of Membranes with a WP-PE SubstrateCoated with Various Blends of Nafion® and EC

This example is similar to Example 7 except that Nafion® (Dupont DE2021,a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer) was usedin the polymer coating blends instead of sPEEK. Four supported membranesamples were prepared by coating the WP-PE substrate with Nafion®, orblends of EC with Nafion®, and properties of the resulting membraneswere tested to determine the effect of increasing the proportion of ECin the blended coating polymer. Sample 8A was prepared by applying athin coating of a Nafion® solution (20% in propanol) to one surface ofthe substrate using a Mayer rod coater. Sample 8B was prepared byapplying a thin coating of a Nafion®/EC solution (0.5 g of EC (48-49.6%ethyl basis) and 0.5 g Nafion® in ethanol, 10% solids). Sample 8C wasprepared by applying a thin coating of a Nafion®/EC solution (0.8 g ofEC (48-49.6% ethyl basis) and 0.2 g Nafion® in ethanol, 10% solids).Sample 8D was prepared by applying a thin coating of a Nafion®/ECsolution (0.9 g of EC (48-49.6% ethyl basis) and 0.1 g Nafion® inethanol, 10% solids). For each membrane sample the coating loading wasdetermined, and the membrane was tested for air crossover, exhaust airtransport ratio (EATR), water permeation (WVTR), using techniquesdescribed herein. The results are shown in Table 8, and are comparedwith the results for Example 7 Sample 7B where the coating was 100% EC.

TABLE 8 (WP-PE substrate) Air EATR EATR Nafion ®/EC Coating cross- 2000500 WVTR Membrane ratio by % loading over cc cc kg/m²/day Sample #weight solids g/m² (cc/min) (%) (%) (50° C.)* 7B  0/100 10% 1.52 0 0 018.2 8A 100/0  20% 2.52 0 0 0 43.4 8B 50/50 10% 1.79 0 0 0 15.4 8C 20/8010% 1.82 0 0 0 16.4 8D 10/90 10% 1.80 0 0 0 19.6 *dynamic WVT test, 33cm² area, 6,000 cm³/min flow, 50% RH in feed

The water transport properties of the membranes comprising a blend ofNafion® and EC were not significantly improved when compared withmembranes comprising Nafion® or EC coatings. Nafion® has a high watervapor permeability; however, Nafion® is costly compared to sPEEK anddemonstrates reduced selectivity at higher relative humidity conditions.

Example 9—Preparation and Testing of Membranes with a DP-PP SubstrateCoated with Various Blends of sPEEK and CA

This example is similar to Example 3 except that a dry stretch processedpolypropylene substrate (DP-PP) was used. A significant performanceincrease was observed with this substrate compared to the othersubstrates tested. This was associated with a clearly observable layerof coating remaining on the membrane surface. In previous trials, asurface layer of coating could not be readily observed. While not beingbound to any particular theory, it is postulated that the pore size andmorphology of the substrate affect whether a coating film is depositedon the surface of the substrate, or whether it impregnates into thesubstrate pores.

In the WP-PE substrates used in Examples 3-8 the surface pore structurewas less defined, had a wider pore size distribution, and the structurewas more fibrous in nature, allowing the polymer in the coating solutionto penetrate into the substrate to a greater extent during the coatingprocess. With DP-PP substrates, the surface pore structure is clearlydefined, there tends to be a smaller average pore size, the pore sizedistribution is narrower, and when coated with a polymer coating, acontinuous surface film was created. This was clearly visible incross-sectional images observed by electron microscope. A well-definedsurface film was not visible in coated WP-PE substrates. The layer ofcoating on the surface of the DP-PP substrates could be observedvisually as a ‘shiny’ or glossy film on the substrate surface as opposedto a more ‘dull’ or matte coating on surface of the WP-PE substrates.

The water permeation (WVTR) of the bare DP-PP substrate was tested (seeSample 9A in Table 9). Seven supported membrane samples were prepared bycoating the DP-PP substrate with sPEEK (DS 63%) or CA (as in Example 3)or blends thereof, and properties of the resulting membranes were testedto determine the effect of increasing the proportion of CA in theblended polymer. Sample 9B was coated with sPEEK only, and was preparedby applying a thin coating of an sPEEK solution (10% sPEEK inacetone/water) to one surface of the substrate using a Mayer rod coater.Sample 9H was coated with CA only, and was prepared by applying a thincoating of a CA solution (10% CA in acetone/water) to one surface of thesubstrate using a Mayer rod coater. In Samples 9C-9H the substrate wascoated with a blend of sPEEK and CA; the percentage by weight of CA inthe polymer blend was increased in 10% increments through Samples 9C-9H.The membrane preparation method was essentially the same for all Samples9C-9H, and the % solids in the acetone/water solution was 10% in eachcase. For each membrane sample the coating loading was determined, andthe membrane was tested for water permeation (WVTR) using techniquesdescribed herein.

TABLE 9 (DP-PP substrate) sPEEK/ Air EATR EATR CA Coating cross- 2000500 WVTR Membrane ratio by loading over cc cc kg/m²/day Sample #weight * g/m² (cc/min) (%) (%) (50° C.)** 9A 0/0 0 0 0 0 43.4 9B 100/0 1.94 0 0 0 39.84 9C 90/10 2.08 0 0 0 39.24 9D 80/20 2.08 0 0 0 40.08 9E70/30 2.13 0 0 0 37.96 9F 60/40 2.07 0 0 0 37.31 9G 50/50 2.43 0 0 035.18 9H  0/100 2.38 0 0 0 26.96 * from acetone/water solution, 10%solids **dynamic WVT test, 33 cm² area, 6,000 cm³/min flow, 50% RH infeed

Even at 50% CA/50% sPEEK, the performance of the blend membranes issignificantly higher than would be expected from a direct ‘rule ofmixture” calculation. Without being bound to any particular theory, itis believed that blending CA with sPEEK leads to morphology changes inthe coating layer, likely due to phase separation on drying, which mayimprove the permeability of the coating layer. Further, the CA blendedin the sPEEK, seems to decrease the swelling of the sPEEK in the coatinglayer, without significantly decreasing the water vapor permeability ofthe coating. An added benefit was that these DP-PP substrate-basedmembrane samples also passed the UL-94HB (horizontal burn) flame testdescribed herein.

Example 10—Contaminant Crossover Under Variable RH Conditions for aDP-PP Substrate Coated with Various Blends of sPEEK and CA

An apparatus was developed to allow controlled humidity on both sides ofthe membrane samples, while allowing controlled generation ofcontaminants in the feed stream of the apparatus. Crossover of aceticacid and ethanol were determined for 3 different coated membrane samplesat RH ranging from 0% to 90% at room temperature (23.3° C.) using DP-PPas a substrate. Sample DP-PP-sPEEK was coated with sPEEK (DS 63%), andwas prepared by applying a thin coating of sPEEK solution (1 g of sPEEKin acetone/water, 10% solids) to one surface of the DP-PP substrateusing a Mayer rod coater. Sample DP-PP-CA was coated with CA (39.7%acetyl content, average M_(N) ca. 50,000), and was prepared by applyinga thin coating of a CA solution (1 g of CA in acetone/water, 10% solids)to one surface of the DP-PP substrate using a Mayer rod coater. InSample DP-PP-sPEEK-CA, the DP-PP substrate was coated with a blend ofsPEEK and CA in a 1:1 ratio (0.5 g of CA and 0.5 g of sPEEK (DS 63%) inacetone/water (10% solids, 5% CA, 5% sPEEK) mixed together at roomtemperature until a clear solution was obtained). The coating processwas completed using a Mayer rod coater. All three membrane samples hadapproximately the same polymer loading and thickness of coating. Theresults of the contaminant crossover tests are shown in Table 10, andare also plotted in the graphs shown in FIGS. 10A and 10B.

TABLE 10 (DP-PP substrate) RH DP-PP-sPEEK DP-PP-sPEEK-CA DP-PP-CA (23.3°C.) Crossover (%) Crossover (%) Crossover (%) RH Acetic Acetic Acetic(%)* Acid Ethanol Acid Ethanol Acid Ethanol 0 0.10 0.07 0.14 0.08 0.290.47 30 0.41 0.40 0.23 0.24 0.44 0.45 50 1.05 0.78 0.54 0.35 0.70 0.4470 2.97 0.90 1.41 0.43 1.09 0.50 90 9.78 11.51 5.84 2.2 4.96 0.70 *ASTMF-739 module (5 cm² area), 600 cm³/min flow, 100-400 ppm VOC

Increasing the RH in the contaminant stream generally increased thecrossover of VOCs (specifically acetic acid and ethanol). Without beingbound to any particular theory, this is believed to be due toplasticization of the membrane coating polymer by water vapor. Asobserved previously, for the membrane coated with sPEEK alone (SampleDP-PP-sPEEK), the contaminant crossover increased significantly at highRH (e.g. above 50% for AA and at 90% for ethanol). However, the membranecoated with a 1:1 blend of sPEEK:CA (Sample DP-PP-sPEEK-CA) showedsignificantly lower contaminant crossover at high RH than theDP-PP-sPEEK sample—closer to the results for the sample with just the CAcoating (DP-PP-CA).

The WVT properties of each of the three Example 10 membrane samples weretested at 50% RH at two different temperatures, using the usingtechniques described herein. The results are reported in Table 11.

TABLE 11 (DP-PP substrate) WVTR [Permeance] Membrane (kg/m²/day) [GPU]Sample 23.3° C., 47% RH* 50° C., 50% RH** DP-PP-sPEEK 4.3 [8200] 37.0[11700] DP-PP-sPEEK/CA 4.1 [7700] 35.8 [11000] DP-PP-CA 3.4 [6100] 28.6[8300]  *ASTM F-739 module (5 cm² area), 600 cm³/min flow **dynamic WVTtest, 33 cm² area, 6000 cm³/min flow

The sample coated with a 1:1 blend of sPEEK:CA (Sample DP-PP-sPEEK/CA)exhibited significantly higher WVTR than the sample with just a CAcoating (DP-PP-CA) at both temperatures. The WVTR values for the samplewith the blended coating (Sample DP-PP-sPEEK/CA) were closer to thosefor the sample with the sPEEK coating (DP-PP-sPEEK).

Data showing the water vapor permeance, and the selectivity for watervapor over acetic acid and ethanol transport, for each of the threeExample 10 membrane samples at different relative humidities (RH) arereported in Tables 12 and 13. Selectivity is determined by dividing thepermeance of water vapor at a given relative humidity and temperature bythe permeance of AA or ethanol at the same relative humidity andtemperature.

TABLE 12 (DP-PP substrate) Water Vapor RH Permeance at (23.3° C.) 23.3°C. (GPU) RH (%) DP-PP-sPEEK DP-PP-sPEEK-CA* DP-PP-CA 30 7488 6448 n/a 508056 7531 6050 70 8415 8056 6368 90 8828 8506 6898 *ASTM F-739 module (5cm2 area), 600 cm3/min flow

TABLE 13 (DP-PP substrate) RH DP-PP-sPEEK DP-PP-sPEEK-CA DP-PP-CA (23.3°C.) Selectivity Selectivity Selectivity RH H₂O/ H₂O/ H₂O/ H₂O/ H₂O/ H₂O/(%)* AA Ethanol AA Ethanol AA Ethanol 30 71 72 108 104 57 55 50 30 40 5483 33 53 70 11 36 22 72 22 49 90 3 3 5 15 5 38 *ASTM F-739 module (5 cm2area), 600 cm3/min flow

As shown in Table 12, the water vapor permeance generally increased withincreasing RH for all three membrane samples. At all RH values tested,the water vapor permeance was significantly lower for the CA coating.The water vapor permeance values for the coating comprising a blend ofsPEEK and CA were closer to the values obtained for the sPEEK-coatedmembrane. As shown in Table 13, the selectivity of all three membranesamples decreased with increasing RH. However, the coating comprising ablend of sPEEK and CA provided better selectivity at all RH conditionsthan the sPEEK coating, and better selectivity than the CA-coatedmembranes under most conditions.

Thus, CA can be incorporated into an sPEEK coating (e.g. sPEEK-CA 1:1)without having a major detrimental impact on WVT. Incorporating CA intoan sPEEK coating lowers contaminant crossover and increases theselectivity of the membrane for water transport when compared tocoatings comprising only sPEEK.

Example 11—Water Uptake Ratios and Water Vapor Sorption

Samples of sPEEK, CA, sPEEK/CA, and Na-sPEEK/CA films were placed inliquid water and then pat dry and weighed to determine the equilibriumliquid water update in these samples at room temperature.

TABLE 14 (Water Uptake) Samples Water Uptake (%) sPEEK 230 sPEEK/CA (1:1wt.:wt.) 170 CA 68 Na-SPEEK/CA (1:1 wt.:wt.) 225

The water uptake observed for the sample comprising a blend of sPEEK andCA is not directly proportion to the “rule of mixture”, but rather has aslightly higher water uptake that is closer to that of the sPEEK sample.This indicates that the CA in the blend membrane does not prevent thesPEEK portion of the film from absorbing water to its full extent and infact improves the overall uptake of the blend film. Compared with thenon-neutralized blend of sPEEK/CA, a blend of neutralized Na-SPEEK andCA (when cast from acetone/water/ethanol) has a higher water uptake,which is of the same magnitude as the sPEEK sample.

The vapor sorption isotherms for the film materials shown in FIG. 11indicate a similar effect indicating the film comprising a blend ofsPEEK and CA (1:1 sPEEK:CA) has water vapor uptake that is similar tothe sPEEK polymer film alone. Vapor sorption tests were completed usinga gravimetric vapor sorption analyzer (Quantachrome) in which the sampleis placed in an isothermal chamber, dried, and then exposed to air undercontrolled relative humidity. The sample is brought to equilibrium andthe total moisture uptake at a given relative humidity and temperatureis recorded. To create a sorption isotherm a series of measurements istaken an isothermal temperature over a range of RHs (i.e. 0% RH to about100% RH). The desorption of water occurs more readily for the filmcomprising a blend of sPEEK and CA than the sPEEK film. The sPEEK filmtends to hold more water on desorption than the sPEEK/CA film, which sicloser in total desorption to the CA film (FIG. 12). Higher water vaporsorption and more desorption from the blend comprising sPEEK and CA isbeneficial where water vapor must be absorbed and then desorbed in orderfor transport to occur through the membrane at given humidityconditions.

Example 12—Humidity Cycling

Membranes were fabricated by coating selective layers comprising sPEEKand a blend of sPEEK and CA (1:1) on a microporous dry-processsubstrate. The membranes were tested for leakage at the beginning oflife (t=0). Samples were placed in an environment chamber where theywere exposed to continuous humidity cycling at 50° C. (between 20 and95% RH). Samples were tested every 100 cycles for leakage. Various otherERV membranes were placed in the environment chamber as well. Allsamples were in triplicate at a minimum; seven samples of the sPEEK andsPEEK/CA coated membranes were used. Table 15 shows maximum leak ratesmeasured for each sample at 3 psi upstream pressure over a 45 cm²membrane area. Increased leak rate over the beginning of life leak rateindicates that damage occurred to the membrane during humidity cyclingtests. Due to the semi-porous nature of the paper-based ERV membranes,they showed some leak at beginning of life.

TABLE 15 (RH Cycling of ERV membranes) Maximum measured pressurized aircrossover (3 psi, 45 cm²) [cm³/min] Samples 0 cycles 100 cycles 200cycles 300 cycles 400 cycles sPEEK 0 13 5 20 22 sPEEK/CA 0 0 0 0 0dPoint Mx4A 0 0 0 0 0 Paper1 1300 2700 30000 — — Paper2 80 630 1280 — —Composite1 0 8300 — — — Film1 0 10000 — — — — indicates that the sampleswere removed from the chamber

It is evident from the RH cycling tests that many commercially availableERV materials cannot withstand RH cycling. However, in use in ERVapplications, such materials will generally be continuously exposed tovariable RH conditions over the lifetime of the material. The sPEEK/CAcoated membranes withstood the RH cycling tests. The sPEEK coatedmembranes do show some leakage after RH cycling, indicating that sPEEKcoated membranes are less robust to humidity cycling conditions thanmembranes coated with a blend of sPEEK and CA. However, the sPEEKleakage is orders of magnitude lower than many commercially availableproducts. Without being bound to any particular theory, it is believedthat the ‘less swellable’ CA reinforces the sPEEK and prevents excessiveswelling and dimensional instability which would otherwise lead todefects and failure over time under RH cycling conditions.

Example 13—Neutralization of Blends of sPEEK and CA to the Sodium Form

Due to the degradation of CA in acidic solutions, and in the sPEEK/CAfilm layer, sPEEK was neutralized (i.e. the sulfonic acid group protonsexchanged for cations). To prepare a neutralized/exchanged Na-sPEEK/CA(1:1) coating solution, 2.5 g of sPEEK and 2.5 g CA were dissolved in80/20 acetone/water and the solution was made up to 90 g (5.6% solidscontent). A solution of 0.5 M NaHCO₃ or NaOH was added drop wise untilthe pH was between about 5 to about 6. The final polymer solids contentwas about 5%. When the coating solution contained 2.5 g of sPEEK, 0.42 gNaHCO₃ was added.

Alternatively, sPEEK may be treated with excess 0.1 M NaOH. sPEEK issoaked in 0.1 M NaOH solution and rinsed with deionized water until thepH of the wash solution is neutral (i.e. pH about 7). The resultingNa-sPEEK is washed with deionized water and dried at 50° C. 2.5 g of theresulting neutralized Na-sPEEK and 2.5 g CA are dissolved in 72.5:27.5acetone/water solution and the solution is made up to 100 g (5% solidscontent).

Films cast from the neutralized/exchanged Na-sPEEK solutions showed noevidence of degradation of the CA. In membranes cast from thesesolutions, no leakage or long term degradation of performance wasobserved and WVT was substantially equivalent to sPEEK/CA membranes madefrom the proton form of the sPEEK.

Example 14—Na-sPEEK and CA Blends Cast from Ternary Solvent Solutions

To reduce or minimize phase inversion and improve Na-sPEEK/CA coating ona DP-PP substrate, a ternary solvent system may be used to formulate aNa-sPEEK/CA coating solution. The ternary solvent system may compriseacetone, water, and ethanol. Na-sPEEK/CA coating solutions wereformulated using different acetone/water/ethanol ratios, whereinacetone/water was 72/28 (wt./wt.) in all samples, the sPEEK was about63% DS, the CA was about 39.7% acetyl content, and the average M_(N) ca.of CA was about 50,000. In each sample coating solution, the sPEEK:CA(wt.:wt.) ratio was about 1:1 and the polymer solids content was about4%. sPEEK was neutralized/exchanged using 0.5 M NaHCO₃ to yieldNa-sPEEK/CA as described elsewhere herein. Membranes were made bycoating each sample solution on a DP-PP substrate. Coating weight was inthe range of about 0.5 g/m² to about 1.5 g/m². Films of the coatingformulated from coating solutions comprising 10 wt. % ethanol or lesshad some discontinuities or evidence of pores induced by phaseinversion. With the exception of the membrane made using a coatingsolution with a 2% solids content, all membranes exhibited zerocrossover leak and zero EATR indicating that defect-free selectivelayers were cast on the DP-PP surface.

TABLE 16 (Ternary solvent systems) Na- Acetone H₂O Ethanol sPEEK CASample (%) (%) (%) (%) (%) DP-Na-sPEEK-CA1 69 27 0 2.0 2.0DP-Na-sPEEK-CA2 68 26 2 2.0 2.0 DP-Na-sPEEK-CA3 67 26 3 2.0 2.0DP-Na-sPEEK-CA4 66 25 5 2.0 2.0 DP-Na-sPEEK-CA5 62 24 10 2.0 2.0DP-Na-sPEEK-CA6 58 22 16 2.0 2.0 DP-Na-sPEEK-CA7 55 21 20 2.0 2.0DP-Na-sPEEK-CA8 55 22 20 1.5 1.5 DP-Na-sPEEK-CA9 56 22 20 1.0 1.0

TABLE 17 (Membrane Performance) Cross- EATR WVT Permeance over (500,(kg/m2/day) (GPU) Sample Film Quality (cm³/min) 2000) (%) 25° C.*** 25°C.*** DP-Na-sPEEK-CA1 Discontinuous* 0 (0, 0) 9.3 11700 DP-Na-sPEEK-CA2Discontinuous* 0 (0, 0) 9.3 11700 DP-Na-sPEEK-CA3 Discontinuous* 0 (0,0) 9.3 11700 DP-Na-sPEEK-CA4 Discontinuous* 0 (0, 0) 9.4 11900DP-Na-sPEEK-CA5 Discontinuous* 0 (0, 0) 9.7 12500 DP-Na-sPEEK-CA6Continuous** 0 (0, 0) 9.5 12100 DP-Na-sPEEK-CA7 Continuous** 0 (0, 0)9.6 12300 DP-Na-sPEEK-CA8 Continuous** 0 (0, 0) 9.7 12500DP-Na-sPEEK-CA9 Continuous** 75 — — — *discontinuous films or films withevidence of clouding, porosity, or phase inversion **clear and uniformfilms with no evidence of clouding ***Dynamic WVT test, 33 cm² area,6000 cm³/min flow, 50% RH in feed

sPEEK polymers have desirable properties for WVT membranes. However,dense films of sPEEK tend to be expensive and often have poordimensional stability under wet conditions. Supporting a thin layer ofsuch polymers on a microporous substrate can impart desirable mechanicalproperties to the resulting membrane, as well as reducing the quantityof costly sPEEK polymer needed for a particular end-use application.Membranes comprising a microporous substrate coated with a thin layer ofsPEEK polymer were found to have desirable properties for ERVapplications, including: high WVT; low transport of other chemicalspecies (VOCs and odors); low air crossover; and ability to cast thesPEEK polymer on higher performance substrates which are also flameresistant. However, at high humidity conditions, these polymers tend toswell, which can increase permeability of VOCs and other undesirablechemical species, reducing the selectivity of the membrane.

In seeking to further reduce the quantity of sPEEK used in the coatedmembranes, sPEEK was blended with a cellulose derivate (which is lessexpensive), and the blended membrane was used as a coating. Surprisinglyit was discovered that membranes comprising some blended polymercoatings exhibited water vapor permeability properties comparable to, oreven better than, membranes comprising a coating made of sPEEK alone(even though the water vapor permeability of the cellulose derivativesare generally substantially lower than those of sPEEK polymers). Thiswas particularly true when sPEEK was blended with CA, as shown in theExamples and test results provided herein. Furthermore, including CA inthe blend tended to decrease the swelling of the coating layer in thepresence high RH in air stream interfacing with the membrane. Thisdecrease in swelling resulted in significantly decreased permeance ofVOCs through the membrane under high humidity conditions, withoutsignificantly compromising the water vapor permeance at all humidityconditions. The membranes with a blended polymer coating alsodemonstrated improved stability under relative humidity cyclingconditions relative to the membranes coated with sPEEK. Furtherexperiments showed that blending CA or other cellulose derivatives withother highly water permeable polymers besides sPEEK, does notnecessarily give a polymer or membrane with desirable properties. Itseems it is not possible to predict the properties of a blended polymerbased on the properties of the individual components in the blend. Thecombination of sPEEK polymers with CA seems to be particularly andunexpectedly advantageous.

ERV Core

ERV cores may be of the type described in applicant's internationalapplication No PCT/CA2012/050918 entitled COUNTER-FLOW ENERGY RECOVERYVENTILATOR (ERV) CORE.

FIG. 13 shows a simplified isometric view of an embodiment of an ERVcore comprising a pleated membrane cartridge 200 which comprisesalternating layers of membrane 201 with gas flow pathways in betweenadjacent layers. The flow pathways can comprise channels that runthrough the core over the surface of the membrane and are sealed suchthat there is flow of gases through the core from one face to the otherwithout mixing of the two streams through the membrane. The gas streamsare directed through pleated membrane cartridge 200 of ERV core suchthat one side of each membrane layer is exposed to one gas stream 210and the opposing side of the membrane layer is exposed to the other gasstream 220. In the illustrated embodiment the gases are in a cross-flowconfiguration. Counterflow, co-flow, and other relative flowconfigurations can be used depending on the geometry of the ERV core andthe manifolding. Transport of heat and moisture occurs through themembrane due to the differential of heat of moisture between the two gasstreams. The flow of heat and moisture may occur in either directionthrough the membranes, depending on the conditions of the gas streams220 and 210. When stream 210 is cool and dry and stream 220 is warm andmoist, heat and humidity transport will occur through the membrane toheat and humidify flow 210 before it exits the core at 211. The warm andmoist flow 220 will thus be cooled and dehumidified as it passes throughthe core and exits at 221.

The perimeter of the pleated membrane cartridge 200 is sealed to preventgases from leaking between the perimeter of the pleated cartridge andthe interior of the ERV housing (not shown in FIG. 13). For example,gaskets or seals 202 and 203 can be disposed along the edges and top andbottom surfaces of pleated membrane cartridge 200 so that once in theERV system a seal will be created between the inlet and outlet ports toprevent short-circuiting of the gases between the streams.

FIG. 14 shows a simplified view of an ERV core 300 in an ERV system 340.System 340 can contain fans and controls to move the air through thesystem in the directions indicated by the arrows in FIG. 14. Seals arecreated around the periphery of the core. The ERV system interfacesbetween air in an enclosed building space 350, and the exteriorenvironment. The seals allow air streams to be directed through ERV core300 in such a way that incoming air 320 entering building 350 passes onone side of the membrane layers in the core 300 and outgoing air 311exiting building 350 passes on the other side of the membrane layers inthe core. If outgoing air 311 is cool and dry and incoming air 320 iswarm and moist, heat and moisture transport will occur through themembrane in the core such that outgoing/exhaust air 310 will have gainedheat and moisture, and incoming air 321 entering building 350 will havebeen cooled and dehumidified.

Methods of Testing

To accurately and consistently coat membranes on a bench-scale, a Mayerrod coater was used. This type of coating device may also be referred toas Meyer bar, miter rod, Meyer rod, meter bar, coating rod, equalizerbar, doctor rod, or metering rod coater. In these types of bars, steelwire is wound tightly around a rod. The gap spacing created betweenadjacent wraps of the wire will depend on the diameter of the wire usedto wrap the rod. In the coating apparatus used in the examples herein,the wire-wound rod is placed at a substantially constant downwardpressure on top of the substrate, and then polymer solution is depositedby pipette onto the substrate surface in front of the rod. A linearactuator drives the rod across the substrate surface at a constant ratespreading the coating on the substrate. The thickness of the wet coatingdeposited on the substrate surface will depend on the diameter of thewire used to wrap the rod. Wire diameters used ranged from 0.05 mm to0.3 mm allowing controlled wet film deposits ranging from about 4 micronto about 24 micron. The coating settles by gravity into a film ofsubstantially uniform wet thickness, after which the material is driedto remove the solvent and create a coated substrate with a consistentdry coating thickness and coating loading. Further refinement in thecoating loading can be achieved by altering the solids content,viscosity, density, and surface tension properties of the solution used.In roll-to-roll processes a slot die or reverse gravure coating methodis preferred.

To assess the air permeation or air crossover properties of the membranematerials in the examples herein, membrane samples were sealed in a testapparatus. Pressurized air was applied to one side of the membrane andthe air flow through the material was recorded. In a typical test, thepressurized air was applied at 3 psi or 20.7 kPa. The crossover flowrate through the test sample was recorded in cubic centimeters perminute (cm³/min). This value can be converted to an air permeation valueby dividing by the applied pressure and the membrane area (45 cm² in atypical test). Air permeation can be reported in cm³/min/cm²/kPa. Unlessotherwise reported, the membrane samples had an air crossover of zero,indicating there were substantially no defects in the coating layer ofthe membrane.

The exhaust air transfer ratio (EATR) provides an indication of theamount of contaminant gas that may pass through the membrane material.It would be desirable for this value to be less than 5%, and moredesirable for it to be less than 1%. Optimally there is 0% contaminantgas transport through the material. A test was developed to determinethe EATR of the membrane. In this test, again a membrane sample wasplaced in a test apparatus which separates the two sides of themembrane, so that independent gas streams may be provided on opposingsides of the membrane. The module had an area of 33 cm² in which gasflow was directed over opposing sides of the membrane in a counter-floworientation, the gases flowing through 7 channels each about 16 cm inlength, 1 mm in depth, and 3 mm in width. On one side of the membrane apure nitrogen stream was passed over the surface of the membrane. On theother side of the membrane an air stream was passed over the membranesurface. The flow rate of the gases over each side of the membrane wasequal in any given test, however transport was measured at two flowrates for each sample, 2000 cm³/min (about 1.6 m/s) and 500 cm³/min(about 0.4 m/s). At lower flow, the residence time of gases flowing overthe membrane surfaces in the module is longer, and higher transportrates can be measured. The transport of oxygen and nitrogen in this testis a measure of defects in the coating layer. Membranes having a coatingwith substantially no defects should have zero EATR at both 2000 cm³/minand 500 cm³/min flow rates. The differential pressure between the twostreams was maintained at zero so that only diffusive transport and notconvective transport occurs through the membrane. An oxygen sensor wasplaced at the outlet of the nitrogen stream to measure the oxygenconcentration. Since the concentration of oxygen in air is known, andthe nitrogen stream contained no oxygen at the inlet, the percentage ofoxygen passing through the membrane by diffusion can be reported as:

EATR %={[C(O₂,1)]/[C(O₂,2)]}×100

where C refers to the percent concentration of oxygen (O₂) at points 1and 2, with point 1 being at the nitrogen-side outlet (measured by thesensor), and point 2 being at the air-side inlet (measured at 20.9%).

A dynamic water vapor transport rate (WVTR) testing procedure wasdeveloped which was designed to test the membranes under conditionswhich are similar to those in which they might be utilized. This testapparatus is similar to that described as a dynamic moisture permeationtest by P. Gibon, C. Kendrick, D. Rivin, L. Sicuranza, and M. Charmchi,“An Automated Water Vapor Diffusion Test Method for Fabrics, Laminates,and Films,” Journal of Industrial Textiles, vol. 24, no. 4, pp. 322-345,April 1995 and also summarized in ASTM E298 and specifically ASTM F2298.A membrane sample was sealed in a test apparatus with flow fieldpathways on both sides of the membrane to evenly distribute gases overthe both surfaces of the sample, the gases being separated by themembrane. The flow rate, temperature, and RH of each inlet gas streamcould be controlled, and the outlet temperatures and RH of each gasstream could be measured. The gases were supplied and directed incounter-flow over the opposing surfaces of the membrane. The membraneactive area in the test jig was 33 cm². In a typical isothermal test, afirst gas stream (sweep stream) was supplied at 50° C. and 0% RH to theinlet on one side on the membrane at 6000 cm³/min (about 0.8 m/s). Asecond gas stream (the feed stream) was supplied to the inlet on theother side of the membrane at 50° C. and 50% RH, and at the same flowrate as the first gas. The water content and temperature of the twostreams were measured and recorded at the outlets. From these values,the water transport rate of the test sample was determined, in units ofmass per time (g/h). The results may also be reported as a water flux bydividing by the membrane area over which the transport has occurred inunits of mass per area per time (kg/m²/h or in units of mol/m²/s). Bydividing flux by the calculated mean vapor pressure differential acrossthe membrane within the test module, a permeance value can be determinedin units of mass per area per time per vapor partial pressuredifferential (mol/m²/s/Pa) and is typically reported in gas permeanceunits (GPU) where 1 GPU=1×10⁻⁶ cm³ (STP) cm⁻² s⁻¹ cmHg⁻¹). Permeance isreported as an apparent permeance without accounting for concentrationboundary layers associated with water vapor at the membrane surfaces.Due to the scale of the results it was found to be most convenient toreport water transport data as a water flux value in units of kg/m²/day.For tests where the temperature and RH were not at the standard testconditions (feed stream at 50° C. and 50% RH), the temperature andhumidity are reported. In some tests the membranes water vapor transportwas measured with the feed stream at 25° C. and 50% RH. In other teststhe feed stream relative humidity was varied.

In order to measure the transport of ‘contaminants’ through ERVmembranes, acetic acid (AA) and ethanol were used as example VOCcontaminants for permeation testing. The permeation method used formeasuring chemical transport in membrane was modified from ASTM F-739:Standard Test Method for Permeation of Liquids and Gases throughProtective Clothing Materials under Conditions of Continuous Contact.Quantitative analysis was performed using a TD-GC system.

Results were reported as a percentage of the contaminant concentrationmeasured in the collection stream over the contaminant concentration inthe supply stream, according to the following equation:

${Transport} = {{\frac{Q_{1}C_{x\; 2}}{Q_{3}C_{x\; 3}}100}\%}$

where Q₁ is the flow rate in the sweep stream (L/min); Q₃ is the flowrate in the feed stream (L/min); C_(x2) is the concentration of xcontaminant in the sweep stream (μg/L); and C_(x3) is the concentrationof x contaminant in the feed stream (μg/L). The module used in this testwas the standard module for the ASTM F-739 test (manufactured by PesceLab Sales). The module had an active area with a diameter of 1″, 0.785in² or 5 cm². In each experiment, gases were supplied at 600 cm³/min oneither side of the membrane. Concentrations of the acetic acid weretypically in the range of 100 to 200 ppm in the feed stream, andconcentrations of ethanol were typically in the range of 200 to 400 ppmin the feed stream.

The flame test used was based on the UL-94HB horizontal burn teststandard from Underwriters Laboratories which is designed to determinethe flammability of a material. A sample of membrane was cut to 1.25cm×12.5 cm. The sample was supported horizontally and then tiltedlengthwise at a 45° angle from horizontal. A propane flame approximatelyone centimeter in height was applied to the lower short edge of thetitled membrane sample. The flame was held to the sample until the flamespread past 2.5 cm of the material. After 2.5 cm of the material burned,the flame was removed and the flame was allowed to propagate across thematerial. The burn time and burn distance were recorded and the burnrate was determined in cm/s. If the material self-extinguished beforethe 10 cm mark and the material has a burn rate of less than 0.125 cm/sthen the material passes the HB test.

The present membranes are particularly suitable for use in enthalpyexchangers, but may also be suitable for other applications involvingexchange of moisture and optionally heat between gas streams with littleor no mixing of the gas streams through the membrane. Such potentialapplications include fuel cell humidifiers, gas drying,dehumidification, medical gas humidification, desalination and airplanehumidification, water filtration, gas separation, and flue gas heat andwater recovery.

The present membranes are preferably coated on just one surface with athin layer of water permeable polymer to give an anisotropic membrane asdescribed above. However, membranes with different properties and watertransport characteristics can be obtained by applying theherein-described coatings to both sides of the substrate, to provide athin surface layer of water permeable polymer formed on both sides ofthe substrate.

The present membranes are preferably coated with a blended polymercomprising sPEEK. sPEEK is of the polyaryletherketone family of polymersand although sPEEK is preferably used in the present membranes, personskilled in the art will recognize that various polyaryletherketones canbe sulfonated and used in a similar manner.

Interpretation of Terms

Unless the context clearly requires otherwise, throughout thedescription and the

-   -   “comprise”, “comprising”, and the like are to be construed in an        inclusive sense, as opposed to an exclusive or exhaustive sense;        that is to say, in the sense of “including, but not limited to”;    -   “connected”, “coupled”, or any variant thereof, means any        connection or coupling, either direct or indirect, between two        or more elements; the coupling or connection between the        elements can be physical, logical, or a combination thereof;    -   “herein”, “above”, “below”, and words of similar import, when        used to describe this specification, shall refer to this        specification as a whole, and not to any particular portions of        this specification;    -   “or”, in reference to a list of two or more items, covers all of        the following interpretations of the word: any of the items in        the list, all of the items in the list, and any combination of        the items in the list;    -   the singular forms “a”, “an”, and “the” also include the meaning        of any appropriate plural forms.

Words that indicate directions such as “vertical”, “transverse”,“horizontal”, “upward”, “downward”, “forward”, “backward”, “inward”,“outward”, “vertical”, “transverse”, “left”, “right”, “front”, “back”,“top”, “bottom”, “below”, “above”, “under”, and the like, used in thisdescription and any accompanying claims (where present), depend on thespecific orientation of the apparatus described and illustrated. Thesubject matter described herein may assume various alternativeorientations. Accordingly, these directional terms are not strictlydefined and should not be interpreted narrowly.

Where a component (e.g. a substrate, assembly, device, manifold, etc.)is referred to above, unless otherwise indicated, reference to thatcomponent (including a reference to a “means”) should be interpreted asincluding as equivalents of that component any component which performsthe function of the described component (i.e., that is functionallyequivalent), including components which are not structurally equivalentto the disclosed structure which performs the function in theillustrated exemplary embodiments described herein.

Specific examples of systems, methods, and apparatus have been describedherein for purposes of illustration. These are only examples. Thetechnology provided herein can be applied to systems other than theexample systems described above. Many alterations, modifications,additions, omissions, and permutations are possible within the practiceof this invention. This invention includes variations on describedembodiments that would be apparent to the skilled addressee, includingvariations obtained by: replacing features, elements and/or acts withequivalent features, elements and/or acts; mixing and matching offeatures, elements and/or acts from different embodiments; combiningfeatures, elements and/or acts from embodiments as described herein withfeatures, elements and/or acts of other technology; and/or omittingcombining features, elements and/or acts from described embodiments.

It is therefore intended that the following appended claims and claimshereafter introduced are interpreted to include all such modifications,permutations, additions, omissions, and sub-combinations as mayreasonably be inferred. The scope of the claims should not be limited bythe preferred embodiments set forth in the examples, but should be giventhe broadest interpretation consistent with the description as a whole.

1. A water vapor transport membrane comprising a microporous substrateand an air impermeable selective layer coated on a first surface of thesubstrate to form a substantially non-porous film thereupon, theselective layer comprising sulfonated polyether ether ketone (sPEEK) andcellulose acetate (CA) in an sPEEK:CA (wt.:wt.) ratio in the range ofabout 7:3 to about 2:3, wherein the acetyl content of the CA is in therange of about 20% to about 62%, the degree of sulfonation of the sPEEKis in the range of about 23% to about 100%, and the selective layer hasa thickness of less than about 5 microns.
 2. A water vapor transportmembrane according to claim 1, wherein the sPEEK comprises sPEEK in acation form.
 3. A water vapor transport membrane according to claim 2,wherein about 80% to about 100% of the sPEEK is in a cation form.
 4. Awater vapor transport membrane according to claim 2, wherein the cationform is a sodium ion form.
 5. (canceled)
 6. A water vapor transportmembrane according to claim 1, wherein the coating loading of theselective layer on the substrate is in the range of about 0.5 g/m² toabout 2.5 g/m².
 7. A water vapor transport membrane according to claim1, wherein the thickness of the selective layer is about 0.75 micron toabout 1.25 microns.
 8. A water vapor transport membrane according toclaim 1, wherein the selective layer is sufficiently flexible to allowpleating of the membrane without fracturing the selective layer.
 9. Awater vapor transport membrane according to claim 1, wherein the watervapor permeance of the membrane is at least 9,000 GPU at temperatures inthe range of about 25° C. to about 50° C.
 10. A water vapor transportmembrane according to claim 1, wherein the acetic acid crossover throughthe membrane is less than about 1% at about 25° C. and about 50%relative humidity.
 11. A water vapor transport membrane according toclaim 1, wherein the membrane selectivity for water vapor over aceticacid is greater than about 50 at about 25° C. and about 50% relativehumidity.
 12. (canceled)
 13. A water vapor transport membrane accordingto claim 1, wherein the substrate is a polyolefin. 14-16. (canceled) 17.A water vapor transport membrane according to claim 1, wherein thesubstrate has a thickness of about 5 microns to about 40 microns. 18.(canceled)
 19. A method for making a water vapor transport membrane, themethod comprising: applying a coating solution or dispersion comprisingsulfonated polyether ether ketone (sPEEK) and cellulose acetate (CA) toa first surface of a microporous substrate and allowing the coatingsolution or dispersion to dry to form an air impermeable selective layeras a substantially non porous film on the first surface of thesubstrate, wherein the coating solution or dispersion comprises ansPEEK:CA (wt.:wt.) ratio in the range of about 7:3 to about 2:3, theacetyl content of the CA is about 20% to about 62%, the degree ofsulfonation of the sPEEK is in the range of about 23% to about 100%; andwherein the selective layer has a thickness of less than about 5microns.
 20. A method according to claim 19, further comprisingexchanging sulfonic acid group protons of the sPEEK for cations.
 21. Amethod according to claim 20, wherein about 80% to about 100% of thesulfonic acid group protons of sPEEK are exchanged for cations.
 22. Amethod according to claim 20, wherein the cations are sodium ions. 23.(canceled)
 24. A method according to claim 19, wherein the solidscontent of the coating solution or dispersion is in the range of about2.5% to about 10% by weight. 25-31. (canceled)
 32. A method according toclaim 19, wherein the substrate is a polyolefin. 33-35. (canceled)
 36. Amethod according to claim 19, wherein the substrate has a thickness ofabout 5 microns to about 40 microns.
 37. (canceled)
 38. An energyrecovery ventilation (ERV) core comprising a pleated membrane cartridge,the membrane cartridge comprising alternating layers of water vaportransport membranes according to claim 1 with gas flow pathways inbetween adjacent membrane layers.
 39. An energy recovery ventilation(ERV) system comprising an ERV core, the ERV core comprising a pleatedmembrane cartridge, wherein the membrane cartridge comprises alternatinglayers of water vapor transport membranes according to claim 1 with gasflow pathways in between adjacent membrane layers. 40-229. (canceled)